ES3009542T3 - Barrier-coated cellulose-based substrate for laminated packaging material - Google Patents

Abstract

The present invention relates to a cellulose-based substrate with a barrier coating (25a) and to a method of manufacturing said cellulose-based substrates, by dispersion coating of a ductile base layer precoat (12a) and subsequent dispersion coating of a gas barrier composition (13a) and/or vapor deposition coating of a barrier deposition coating (14a). (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Cellulose-based substrate with barrier coating for laminated packaging material

Technical field

The present invention relates to a barrier coated paper or cellulose-based substrates for use as a barrier sheet in a laminated packaging material for oxygen-sensitive products, and to a method of manufacturing the barrier coated paper or cellulose-based substrate by applying a barrier dispersion coating, by means of dispersion or solution coating on the ductile base layer, pre-coating and a barrier deposition coating, applied by means of a vapor deposition method at a total thickness of 2 to 5000 nm.

Background of the invention

Single-use, disposable packaging containers for liquid foods are often manufactured from a packaging laminate based on carton or paperboard. One such common packaging container is marketed under the trademark Tetra Brik Aseptic® and is primarily used for the aseptic packaging of liquid foods such as milk, fruit juices, etc., marketed for long-term storage at ambient temperatures. The packaging material in this known packaging container is typically a laminate comprising a main or core layer of paper, carton, or other cellulose-based material, and outer liquid-impermeable layers of thermoplastics. In order to render the packaging container gas-impermeable, in particular oxygen-impermeable, for example, for the purpose of aseptic filling and packaging of milk or fruit juice, the laminate in these packaging containers typically comprises at least one additional layer, most commonly an aluminum foil.

On the inside of the laminate, i.e., the side intended to face the packaged food contents of a container produced from the laminate, there is an innermost layer applied over the aluminum foil. This innermost layer may be composed of one or more partial layers, comprising heat-sealable thermoplastic polymers, such as adhesive polymers and/or polyolefins. Also on the outside of the main layer is an outermost heat-sealable polymer layer.

Packaging containers are generally produced using modern, high-speed packaging machines that form, fill, and seal packages from a web or prefabricated blanks of packaging material. Packaging containers can thus be produced by transforming a web of laminated packaging material into a tube by joining both longitudinal edges of the web together in an overlapping seam, welding the inner and outer heat-sealable thermoplastic polymer layers together. The tube is filled with the intended liquid food product and then divided into individual packages by repeated transverse seals of the tube at a predetermined distance from each other below the level of the tube contents. The packages are separated from the tube by incisions along the transverse seals and are given the desired geometric configuration, usually parallelepiped, by forming creases along fold lines prepared in the packaging material.

The main advantage of this continuous tube-form-fill-seal packaging method concept is that the band can be continuously sterilized just prior to tube formation, thus providing the possibility of an aseptic packaging method, i.e., one in which bacteria are reduced in the liquid contents to be packaged, as well as in the packaging material itself, and the filled packaging container is produced under clean conditions, so that the filled package can be stored for a long time, even at room temperature, without the risk of microbial growth in the packaged product. Another important advantage of the Tetra Brik® type packaging method is, as mentioned above, the possibility of continuous high-speed packaging, which has a considerable impact on profitability.

Packaging containers for sensitive liquid foods, for example, milk or juice, can also be produced from sheet-shaped blanks or prefabricated blanks of the laminated packaging material of the invention. From a tubular blank of the packaging laminate that is folded flat, the packages are produced by first constructing the blank to form an open tubular container capsule, one of whose open ends is closed by folding and heat-sealing integral end panels. The thus closed container capsule is filled with the food product in question, for example, juice, at its open end, which is then closed by further folding and heat-sealing of corresponding integral end panels. An example of a packaging container produced from sheet-shaped and tubular blanks is the so-called conventional gable-roof package. Such packages also exist that have a molded lid and/or a plastic screw cap.

A layer of aluminum foil in the packaging laminate provides gas barrier properties far superior to most other gas barrier materials. Conventional aluminum foil-based packaging laminate for aseptic packaging of liquid foods remains the most cost-effective packaging material, in terms of performance, available on the market today.

Any other material that competes with film-based materials must be cost-effective in terms of raw materials, have comparable food preservation properties, and have comparatively low complexity in converting materials into a finished packaging laminate.

Among the efforts to develop non-aluminum foil materials for liquid food carton packaging, there is also a general incentive toward the development of prefabricated films or sheets that have high and multiple barrier functionalities, that can replace the aluminum foil barrier material in conventional laminated packaging material, or that can combine several separate barrier layers in the laminated material and adapt it to conventional lamination and manufacturing processes.

Preferred types of such alternative, more environmentally sustainable barrier materials are barrier-coated paper substrates manufactured by aqueous dispersion coating or vapor deposition coating on thin paper carrier substrates. Various aqueous dispersion coating processes and vapor deposition coating processes and material recipes for such coatings exist, and there is a need for cost-effective, non-foil, non-aluminum foil barrier materials of this type that have improved barrier properties, particularly against gases such as oxygen gas, for use in packaging laminates for the packaging of liquid foods.

A previous patent publication WO2011/003565A1 discloses a non-foil packaging material comprising a pre-coated and metallized Krahft paper substrate for induction heat sealing purposes.

Previous patent publication WO2017/089508A1 discloses how improved barrier properties can be obtained from a metallized paper in a similar packaging laminate by selecting a paper substrate that provides optimal properties. Such a metallized paper substrate not only provided improved barrier properties but also indicated improved stability of the metallized layer for induction heat sealing purposes.

However, there remains a need for even better oxygen gas barrier properties than those of prior art gas barrier-coated paper substrates. There is also a growing need for improved recyclability and environmental sustainability of the materials used for gas barrier-coated paper substrates and laminated packaging materials containing them.

Disclosure of the invention

Accordingly, an object of the present invention is to provide improved barrier coated cellulose-based substrates for laminating to packaging materials.

It is also an object of the invention to provide barrier-coated papers or cellulose-based substrates that provide good gas barrier properties, as well as improved recyclability and sustainability, which meet the needs of future sustainable laminated packaging materials.

A further general object of the invention is to provide barrier coated papers or cellulose based substrates for improving laminated packaging materials for oxygen sensitive products, such as non-foil laminated packaging materials for liquid, semi-liquid or moist food products, which do not contain aluminum foil but still have good gas and other barrier properties, suitable for long term and aseptic packaging at a reasonable cost.

A particular object is to provide barrier-coated papers or cellulose-based substrates that enable, relative to foil barrier materials, cost-effective non-foil, paper- or board-based laminated packaging materials and containers with good gas and water vapor barrier properties, as well as a sustainable recyclability and environmental profile, in order to manufacture containers for long-term aseptic storage of food.

Therefore, these objects are attainable, according to the present invention, by the barrier-coated cellulose-based substrate and the method of manufacturing the barrier-coated cellulose-based substrate, as defined in the appended claims.

Summary of the invention

According to a first aspect of the invention there is therefore provided a barrier coated cellulose-based substrate for use as a barrier sheet in a laminated packaging material for oxygen-sensitive products, comprising a cellulose-based substrate with a density of at least 900 kg/m and a basis weight of 30 to 80 g/m, and at least one gas barrier coating of at least one gas barrier material at a total thickness of 2 to 7000 nm, such as 2 to 5000 nm, such as 2 to 4000 nm, the gas barrier material excluding nanocrystalline cellulose, NCC, is applied on a first side of the cellulose-based substrate. gas barrier coating, therefore being the cellulose-based substrate with barrier coating suitable for providing gas barrier properties in a laminated packaging material and in packages manufactured therefrom.

The at least one gas barrier coating is a dispersion barrier coating, applied by dispersion or solution coating of an aqueous gas barrier composition over the ductile base coat precoat, and a deposition barrier coating, applied by a vapor deposition method.

In one embodiment, the barrier dispersion coating comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of polyvinyl alcohol, PVOH and ethylene vinyl alcohol, EVOH, starch and starch derivatives, xylan, xylan derivatives, nanofibrillar cellulose/microfibrillar cellulose, NFC/MFC, and combinations of two or more thereof.

The barrier deposition coating comprises a vapor deposition coating of a material selected from metals, metal oxides, inorganic oxides, and carbon coatings and is applied at a thickness of 5 to 200 nm. In one embodiment, the barrier deposition coating is a vapor deposition coating selected from the group consisting of an aluminum and aluminum oxide metallization coating, AIOx, and is preferably an aluminum metallization coating.

The at least one gas barrier coating comprises a barrier dispersion coating, first applied by means of dispersion or solution coating on the ductile base layer, pre-coating and a barrier deposition coating, subsequently applied by means of a vapor deposition method, on the barrier dispersion coating, the barrier dispersion coating being applied in a total amount of 0.2 to 5 g/m2, by dry weight.

The ductile base coat precoat is obtained from an aqueous latex composition, such as a latex selected from the group comprising styrene-butadiene latex (SB latex), methylstyrene-butadiene latex, styrene acrylate latex (SA latex), acrylate latex, such as vinyl-acrylic copolymers and vinyl acetate acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadieneacrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, mixtures thereof or bio-derived latex made from polymeric materials of plant origin.

The ductile base coat precoat is made from material sources of primarily plant origin, by producing an aqueous latex composition comprising an emulsion of a polymeric binder material of biological origin, such as selected from the group comprising starch derivatives, including modified starches and crosslinked starches, polyisoprene, lignin-based polymers, alginates and gums, such as guar gum and soy-based proteins.

The ductile basecoat precoat may be made from an aqueous composition comprising a polymeric binder material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymer latex (SB), styrene acrylate copolymer latex (SA), other acrylate polymer and copolymer latexes, such as vinyl-acrylic copolymer latex and acrylate vinyl acetate copolymer latex.

The ductile basecoat precoat may advantageously further comprise a filler material to further smooth the surface of the cellulose-based substrate. The filler may be an inorganic material and, in a preferred embodiment, may comprise layered particles of an inorganic compound. These layered fillers may further contribute to the barrier properties of the material by creating overlapping mineral sheets or flakes, thereby preventing the migration of small molecules through the material. Such layered inorganic particles may be clays, such as kaolin clay and/or bentonite clays, silicates, and talc particles.

In one embodiment, the ductile basecoat precoat is applied by means of aqueous dispersion coating in an amount of 2 to 15 g/m2, such as 5 to 15 g/m2, such as 8 to 15 g/m2, such as 10 to 15 g/m2, by dry weight.

The cellulose-based substrate may further have a second ductile coating on its opposite side, which may be of the same type as the ductile base layer precoat on the first side of the substrate.

The barrier-coated cellulose-based substrate of the invention may be used in a laminated packaging material, which may further comprise a first, outermost layer of liquid-impermeable material and a second, innermost layer of liquid-impermeable material. The second, innermost layer of liquid-impermeable material forms the contact layer toward the product to be packaged in a packaging container formed from the laminated packaging material and may also be heat-sealable to itself or to other thermoplastic materials.

The laminated packaging material may further comprise an additional layer of paper or cardboard or other cellulose-based material, constituting a main layer.

Therefore, for the purpose of carton packaging of oxygen-sensitive food products, such as liquid, semi-liquid or moist food products, such a laminated packaging material may comprise a main layer of paper or board or other cellulose-based material, a first outermost layer of liquid-impermeable material, a second innermost layer of liquid-impermeable and optionally heat-sealable material and, arranged on the inner side of the main layer, between the main layer and the second innermost layer, the barrier-coated cellulose-based substrate of the first aspect.

Such a laminated packaging material can be used in a packaging container, which can be intended for packaging liquid, semi-liquid, or moist foods. Such a packaging container is manufactured at least in part from the laminated packaging material, or is made entirely from the laminated packaging material.

In a second aspect of the invention, there is provided a method of manufacturing the barrier coated cellulose-based substrate of the first aspect. The method comprises a first step of providing a cellulose-based substrate, having a first side and a second side, as a moving web in a roll-to-roll system, a second step of applying a first aqueous dispersion of a ductile basecoat precoat composition onto the first side of the cellulose-based moving substrate, optionally applying a second aqueous dispersion of a ductile coating composition onto the other side of the moving substrate and subsequently drying the applied ductile basecoat precoat, and the optional second ductile coating composition, by forced evaporation, a third step of calendering the dried, precoated cellulose-based substrate to obtain a density of at least 900 kg/m3, such as at least 1000 kg/m3, and a fourth step.

comprising a first step of applying a gas barrier coating by dispersion coating a second dispersion or solution of a barrier composition, onto the first side of the movable cellulose-based substrate with the ductile base layer precoat, and drying the applied gas barrier coating by forced evaporation, and a second subsequent step of vapor deposition of a barrier coating onto the first side of the movable cellulose-based substrate with the ductile base layer precoat and the gas barrier coating of the first step, at a total gas barrier coating thickness of 2 to 7000 nm, such as 2 to 5000 nm.

Heretofore, it has been assumed that improved gas barrier properties can be achieved from barrier-coated papers by obtaining improved cellulose-based substrates, which inherently provide gas barrier properties when laminated to any polymer layer, and/or by coating them with thicker layers of the barrier coating materials that have inherent gas barrier properties. However, it has recently been realized that the interface portion between the barrier coatings and the cellulose-based substrate can play a key role in the optimal performance of the subsequently applied coatings, which contribute the most to the gas barrier properties. It has been discovered that optimal performance can be achieved by adding a ductile base layer precoat over the surface of the high-density cellulose-based substrate. By doing so, it has been observed that the barrier qualities of the cellulose-based substrate itself need not be as high, and the amount of gas barrier polymer coating as a barrier precoat can even be reduced. Therefore, the resulting gas barrier properties of a packaging laminate will be enhanced if a ductile base coat precoat is used, even though it does not itself contribute significant gas barrier properties; that is, the gas barrier properties are not inherent to the ductile base coat precoat material(s). The ductile base coat precoat composition should be selected to provide a ductile base as well as a uniform, dense, and compliant precoat surface to receive any additional gas barrier coating. However, the material selected for the ductile base coat precoat need not contribute inherent gas barrier properties.

The ductile basecoat precoat material is advantageously applied in the form of an aqueous composition comprising a polymeric binder material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymer latex (SB), styrene acrylate copolymer latex (SA), other acrylate polymer and copolymer latexes, such as vinyl-acrylic copolymer latex and vinyl acetate acrylate copolymer latex, and polymeric materials of biological origin. The first aqueous dispersion of the ductile basecoat precoat composition may further contain a filler material, such as clay or other inorganic particles or pigments, and/or cellulose fibrils.

The barrier-coated cellulose-based substrate obtained by the above-described method and coating layer configuration provides enhanced gas barrier properties to a laminated packaging material as well as to packaging containers made therefrom, and can also improve the recyclability and sustainability profile of such packaging materials and packaging containers.

Detailed description

By the term "long-term storage" as used in connection with the present invention, it is meant that the packaging container must be able to preserve the qualities of the packaged food product, i.e. nutritional value, hygienic safety and taste, under ambient conditions for at least 1 or 2 months, such as at least 3 months, preferably longer, such as 6 months, such as 12 months or more.

The term "package integrity" generally refers to the impermeability of the package, i.e., the resistance to leakage or breakage of a packaging container. The term encompasses the package's resistance to the intrusion of microbes, such as bacteria, dirt, and other substances, which can deteriorate the packaged food product and shorten the expected shelf life of the package.

An important contribution to the integrity of a package made from a laminated packaging material is good internal adhesion between adjacent layers of the laminated material. Another contribution comes from the material's resistance to defects, such as pores, tears, and the like, within each of the material layers themselves. Another contribution comes from the strength of the sealing seams, by which the material seals itself to form a packaging container. Regarding the laminated packaging material itself, the integrity property primarily focuses on the adhesion of the respective laminate layers to their adjacent layers, as well as the ability of the individual material layers to withstand thermal and mechanical loads, for example, during folding and sealing to form packaging containers. Regarding the sealing of the packages, integrity primarily focuses on the quality of the sealing seams, which is ensured by robust sealing operations that function well on filling machines, which in turn is ensured by appropriately adapted heat-sealing properties of the laminated packaging material.

The term "liquid or semi-liquid food" generally refers to food products that have a fluid content that may optionally contain food pieces. Dairy and milk, soy, rice, cereal and seed beverages, juice, nectar, still beverages, water, flavored water, energy drinks, sports drinks, coffee or tea beverages, coconut water, wine, soups, jalapeños, tomatoes, salsa (such as pasta sauce), beans, and olive oil are some non-limiting examples of the food products covered.

Additional examples of other oxygen-sensitive food products that can be packaged and protected with the laminated packaging materials of the present disclosure are, for example, dry and/or fatty foods, such as powdered milks and other powdered foods. Examples of fatty foods include cheese, butter, and spreads. Such packaging may be flow-wrap or form-fill-seal (FFS) packaging, for example, pouches. It may also be a jar, tray, lidded spread, collapsible tube, clamshell package, sleeve, sachet, or wrapper. In these applications, the packaging material typically experiences folding or similar stress (e.g., bending, stretching), making the packaging material based on the barrier-coated cellulose-based substrate of the present disclosure particularly suitable.

The term "aseptic" in relation to a packaging material and a packaging container refers to the conditions under which microorganisms are killed, inactivated, or destroyed. Examples of microorganisms include bacteria and spores. Generally, an aseptic process is used when a product is aseptically packaged in a packaging container. For continued asepsis throughout the shelf life of the package, the integrity properties of the package are, of course, very important. For the long-term shelf life of a packaged food product, it may also be important for the package to have barrier properties against gases and vapors, such as oxygen gas, in order to preserve its original flavor and nutritional value, such as, for example, its vitamin C content.

The term "main layer" generally refers to the thickest layer or the layer containing the largest amount of material in a multilayer laminate, i.e., the layer that contributes most to the mechanical properties and dimensional stability of the laminate and the structural stability of the packaging containers obtained by folding from the laminate, based on thick paper, board, or cardboard. It can also mean a layer providing a greater thickness spacing in a sandwich structure, which additionally interacts with the stabilizing coating layers, which have a higher Young's modulus, on either side of the main layer, in order to achieve sufficient mechanical properties, such as flexural rigidity, to achieve the structural stability of the formed packaging containers.

As used herein, the term "dispersion coating" refers to a coating technique in which an aqueous or substantially aqueous dispersion, suspension, emulsion, or solution of a polymer is applied to the surface of a substrate layer, typically in the form of a continuous web, to form a solid, substantially non-porous film after drying. Therefore, the term "dispersion" also encompasses any suspension, emulsion, or solution, or mixtures thereof, that would be capable of providing such a coating after drying. Polyvinyl alcohols (PVOH, PVAL) are typical polymers suitable for dispersion coating, but, for example, in the case of high degrees of saponification, in practice, they may rather be polymer solutions or mixtures of dispersed and dissolved PVOH. A dispersion-coated barrier layer or coating is formed by dispersion coating techniques, also referred to as "liquid film coating." Aqueous dispersions may comprise fine polymer particles and thus be a latex.

The term "latex" as used herein refers to a composition comprising an aqueous suspension or dispersion or emulsion of polymer particles, which may be natural polymers, synthetic polymers, synthetic polymers derived from biomasses, or combinations thereof.

The paper weights were determined according to the official test method of ISO 536:2019 using the unit g/m2, while the thickness and density were determined according to ISO 534:2011, using the units pm (m) and kg/m3, respectively.

Thickness measurements of polymer layers coated on paper can be measured and estimated by taking samples of cut sections of the structure and examining them under an SEM microscope. Sectioning can be performed, for example, using a cryomicrotome.

The TTO was measured using an Oxtran 2/21 (Mocon) coulometric sensor and evaluated according to ASTM F1927-14 and ASTM F1307-14. See Examples for a more detailed description of the TTO test methods.

The method for determining the TTO in flat material identified the amount of oxygen per surface area and unit of time passing through a material at a defined temperature, a given atmospheric pressure, i.e., at a 21% oxygen atmosphere (unless otherwise stated), for 24 hours. The method for determining the TTO in packaging identified the amount of oxygen per unit of time entering the packaging at a defined temperature, a given atmospheric pressure, i.e., at a 21% oxygen atmosphere (unless otherwise stated), for 24 hours.

Water vapor transmission rate (WVTR) measurements were made using a Permatran 3/33 (Mocon) instrument (standard: ASTM F1249-13 using a modulated infrared sensor for relative humidity detection and WVTR measurement) at 38 °C and a 90% impulse relative humidity gradient.

The surface roughness was measured according to TAPPI standard 555 om-15, which is the same as ISO standard 8791 4. The cellulose-based substrate suitable for carrying barrier coatings for the purposes of the invention is not limited to a certain type of paper, but also includes other cellulose-based substrates, based on any type of native cellulose, fibrous or micro/nanofibrillar cellulose with varying degrees of crystallinity. The invention is not applicable, however, to plastics or polymer substrates, such as films made from regenerated, i.e. dissolved and subsequently precipitated, chemically modified cellulose polymers.

It has been observed that the combination of a base coat precoat and a gas barrier coating or coatings, such as those of the present invention, can improve the gas barrier properties of a paper substrate beyond what was heretofore thought possible.

To be suitable for a final barrier coating step by means of a vapor deposition coating process, the fibrous portion of a substrate should be thin, such as 60 g/m2 or less, such as 50 g/m2 or less, preferably 45 g/m2 or less, for reasons of production efficiency and economy and to avoid blistering of the coating due to air being trapped in a cellulose-based fibrous portion of a substrate. On the other hand, thinner cellulose-based substrates or with a basis weight below 30 g/m2 may be mechanically too weak and/or less dimensionally stable when coated with wet dispersions and subsequently dried, thus presenting problems of shrinkage or curling or even web breaks. Therefore, it is more preferred to use cellulose-based substrates having a grammage of 30 to 70 g/m2, such as 30 to 65 g/m2, such as 35 to 60 g/m2, such as 35 to 55 g/m2, such as 2 to 50 g/m35.

Furthermore, the precoated cellulose-based substrate has a high density of at least 900 kg/m3 and must also have a dense and smooth surface, for the best possible interface with an additional gas barrier coating applied to it. Consequently, the barrier-coated cellulose-based substrate must be a precoated and calendered paper, such as a supercalendered precoated paper. The calendering or supercalendering operation, in addition to increased substrate density, also achieves improved bonding between, or "integration of," the precoat layer and the surface of the paper substrate.

The cellulose-based substrate for use according to the invention may be formed from cellulose fibers comprising at least 50% by dry weight of chemical pulp, such as sulfate pulp. The chemical pulp is used to obtain toughness in a paper for high-speed coating and converting processes and for use in final packaging.

Sulfate or Kraft pulp can be advantageous for improving repulping in recycling and general fiber dewatering.

In order to be recyclable and have good dewaterability, cellulose-based substrate fibers must have a Canadian Standard Freedom (CSF) of greater than 300 ml, such as greater than 350 ml, such as greater than 400 ml, as measured by ISO 5267-2:2001. Correspondingly, cellulose-based substrate fibers must have a Schopper-Riegler value of less than 40 degrees SR, such as less than 36 degrees SR, such as less than 32 degrees SR, as measured according to ISO 5267-1:1999.

The softwood pulp can provide strength/toughness properties to the resulting paper and can be contained in the pulp at least 50% by weight. Preferably, therefore, the cellulose-based substrate comprises at least 50% by weight, such as 60 to 100% by weight, such as 70 to 100% by weight of Kraft softwood pulp, such as bleached Kraft softwood pulp.

It has been observed that for some applications, such as liquid-impermeable packaging of wet, liquid or viscous fluid products, it may be advantageous to use as thin a cellulose-based substrate as possible, because then less polymer might be needed in adjacent liquid-impermeable layers or in layers of heat-sealable material.

In order to obtain optimal barrier properties by means of a minimum amount of barrier material, it has so far been found that a gas barrier coating, which has to be coated to a thickness of only a few micrometers or nanometers, on a paper or cellulose-based substrate, needs an additional base of a ductile base layer precoat which has to be applied first to the cellulose-based substrate.

The ductile base coat precoat may be obtained from an aqueous composition comprising a polymeric binder material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymer latex (SB), styrene acrylate copolymer latex (SA), other polymer latexes and acrylate copolymers, such as vinyl-acrylic copolymer latex and acrylate vinyl acetate copolymer latex.

The ductile base coat precoat may be obtained from an aqueous latex composition comprising a bio-derived polymeric binder material having inherent ductility properties, selected from the group comprising derivatives of starch, polyisoprene, lignin-based polymers, alginates, soy-based gums and proteins, and latex of one or more of said bio-derived polymeric binder materials.

The ductile base coat precoat may further comprise a filler material.

The ductile basecoat precoat may be applied by suitable dispersion coating techniques such as knife coating, rod coating, bar coating, smooth roll coating, reverse roll coating, lip coating, air knife coating, curtain flow coating, dip coating methods and wide slot nozzle coating, and subsequent drying to evaporate the dispersion medium, usually water, by forced convection drying. Preferably, the ductile basecoat precoat is applied by knife or rod coating technology and subsequent drying. The term aqueous dispersion coating includes the coating of aqueous compositions of emulsions, dispersions, suspensions, solutions and polymeric latex formulations, and also when such compositions further comprise pigments, inorganic particles or other filler material.

The ductile base coat precoat is obtained from an aqueous latex composition, such as a latex selected from the group comprising styrene-butadiene latex (SB latex), methylstyrene-butadiene latex, styrene acrylate latex (SA latex), acrylate latex, such as vinyl-acrylic copolymers and vinyl acetate acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadieneacrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, mixtures thereof or bio-derived latex made from polymeric materials of plant origin. Furthermore, for example, styrene-acrylate latex or styrene-butadiene latex can be derived, at least in part, from biomass to provide similar performance with an improved carbon footprint.

In one embodiment, the ductile basecoat precoat may be made from substantially plant-derived material sources, by producing an aqueous latex composition comprising an emulsion of a bio-derived polymeric binder material, such as selected from the group comprising starch derivatives, including modified starches and crosslinked starches, polyisoprene, lignin-based polymers, alginates, and gums, such as guar gum, and soy-based proteins, including latex compositions of the type "Ecosphere" from Ecosynthetix, "Vytex" from Vystar, "NeoLigno" from Stora Enso, "OC-Binder" from Organoclick, "Polygal" surface coatings from Polygal. The Ecosphere® biolatex composition from Ecosynthetix is, for example, an aqueous latex of crosslinked starch particles. A latex may be manufactured by aqueous emulsion polymerization. Alternatively, as in the case of producing a latex from a biopolymer, the biopolymeric material, such as starch, can be plasticized under shear force to a suitable particle size and subsequently crosslinked by adding a crosslinking agent. The biopolymer particles can then be added to a water dispersion to form an aqueous latex or particle suspension.

Thus, in one embodiment, the ductile basecoat precoat composition may be made from a polymer of plant or biological origin and applied in the form of an aqueous latex of said polymer.

Therefore, the ductile basecoat precoat may be made of an aqueous latex composition comprising a polymeric material having inherent ductility properties selected from the group consisting of styrene-butadiene copolymers (SB), styrene acrylate copolymers (SA), other acrylate polymers and acrylate copolymers, such as vinyl-acrylic copolymers and vinyl acetate and acrylate copolymers, and aqueous latexes of bio-derived polymeric materials.

In a further embodiment, the ductile basecoat precoat may be made from an aqueous latex composition comprising a bio-derived polymeric material having inherent ductility properties selected from the group comprising starch derivatives, including modified starches and crosslinked starches, polyisoprene, lignin-based polymers, alginates, gums, and soy-based proteins.

In a still further embodiment, the ductile base coat precoat may be made from an aqueous latex composition comprising crosslinked starch particles.

The latex composition may further comprise inorganic filler particles, such as kaolin clay or other layered clay compounds, silica particles, talc and/or calcium carbonate particles, from 1 to 80% by weight of the dry content, such as from 1 to 70% by weight, such as from 1 to 50% by weight, such as from 1 to 40% by weight, such as from 30% by weight, such as from 1 to 20% by weight of the dry content. The filler content may further promote ductility while providing sufficient flexibility and reducing stresses in the precoat such that the precoat can follow the cellulose-based portion of the substrate as it is folded, without causing cracks in the precoat itself.

The latex composition may alternatively, or in addition, comprise organic filler material, such as microfibrillated cellulose.

In one embodiment, the ductile basecoat precoat may comprise 4 to 45 wt.-%, such as 4 to 35 wt.-%, such as 4 to 25 wt.-%, such as 4 to 20 wt.-%, such as 4 to 16 wt.-% of the polymeric binder material having inherent ductility properties, and 55 to 96 wt.-%, such as 65 to 96 wt.-%, such as 75 to 96 wt.-%, such as 80 to 96 wt.-% of the filler material, on a dry weight basis, and optionally additional compounds, such as thickening agents and crosslinking compounds, in amounts of additives. Such amounts of additives would be included only up to 10 wt.-% of the ductile basecoat precoat, on a dry weight basis.

In another embodiment, the ductile basecoat precoat may comprise 10 to 20% by weight of the polymeric binder material having inherent ductility properties, 75 to 85% by weight of an inorganic filler, 3 to 5% by weight of a crosslinking compound, such as starch, and 1 to 2% by weight of a thickening agent, based on dry weight.

The filler material may be an inorganic filler selected from the group comprising clays, such as nanoclays, including bentonite clays, kaolin clay, talc, CaCO3 and silica particles.

Preferably, the filler material may be an inorganic layered compound, such as bentonite clay or kaolin clay. Particularly suitable layered clay minerals may be laponite, kaolinite, dichite, nacrite, halloysite, antigorite, chrysotile, pyrophyllite, montmorillonite, hectorite, saponite, sauconite, sodium tetrasilicate mica, sodium taeniolite, common mica, marguerite, vermiculite, phlogopite, xanthophyllite and the like. A specific type of such layered nanoclay particles are montmorillonite particles, e.g., sodium-exchanged montmorillonite (Na-MMT).

The ash content of the cellulose-based substrate precoated in this way can therefore be 15 to 25% by weight, such as 15 to 23% by weight, as determined by ISO 1762:2019. The same ash content range applies to a cellulose-based substrate with a gas barrier coating and precoating, i.e., 15-25% by weight.

The ductile basecoat precoat composition is applied at a basis weight of 2 to 15 g/m2, such as 5 to 15 g/m2, such as 8 to 15 g/m2, such as 10 to 15 g/m2, by dry weight.

The ductile basecoat precoat polymer may be selected to have a glass transition temperature of -30 to 30 degrees Celsius, such as -30 to 20 degrees Celsius, to provide inherent ductility to a paper substrate coated with a basecoat precoat thereof.

The cellulose-based substrate may further have a second ductile coating on its opposite side, which may be of the same type as the ductile base layer precoat on the first side of the substrate.

The second ductile coating composition may be applied by aqueous dispersion coating in an amount of 1 to 10 g/m2, such as 1 to 7 g/m2, such as 1 to 6 g/m2, such as 1 to 5 g/m2, such as 2 to 5 g/m2, by dry weight. Particularly suitable latex compositions may be described as those having a chemical composition of a latex polymer, a styrene-butadiene copolymer, or a styrene-acrylic copolymer. Such latex polymers are miscible with water in any proportion. Other particularly suitable latex polymers may be anionic aqueous dispersions of copolymers of n-butyl acrylate and styrene.

The ductile base layer precoat should be applied directly onto and adjacent to the surface of the paper- or cellulose-based substrate. The paper may allow moisture to migrate outward through the laminated packaging material, and the ductile base layer precoat material may also allow such water vapor migration, to prevent unfavorable moisture retention near a moisture-sensitive barrier coating, e.g., PVOH or EVOH. Any moisture that migrates through the material from the interior of the liquid food product in the package will additionally be slowly transported through the paper layer and the main paperboard layer of the laminated packaging material to the exterior of the packaging container. The cellulose-based substrate and the main paperboard layer can then "breathe" moisture from the barrier precoat and thereby maintain the moisture content within the gas barrier coating(s) substantially constant over time.

The ductile basecoat precoat may be calendered after coating onto the cellulose-based substrate and forced convection drying. A calendering operation further integrates the ductile basecoat precoat with the cellulose surface of the substrate, improving surface bonding while creating a smooth surface of the ductile basecoat precoat. The calendering operation may be a supercalendering operation involving multiple high-pressure roll nips and at least one heated roll nip, such as more than four high-pressure roll nips, such that the density of the precoated cellulose-based substrate may be increased to at least 900 kg/m3, such as above 1000 kg/m3, such as above 1100 kg/m3. The heated roll temperature may provide a surface temperature of 100 to 300 °C, such as 100 to 240 °C.

The solids content in the applied aqueous latex coating may be in the range of 45 to 70% by weight, such as 45 to 60% by weight, such as 47 to 55% by weight, such as 48 to 51% by weight.

The most suitable system type for dispersion coating of precoating or ductile coating compositions are knife coaters or stick coaters, where a large amount of coating composition is applied to the paper and the excess is scraped off again. The coating composition is applied to the substrate by an applicator. Common applicators include jet applicators, roller applicators, and short residence time applicators (SDTA). An advantage of roller applicators is that poor substrate paper formation is less critical for the roller applicator, making it ideal when thick coatings are desired. The knives used to scrape off the excess coating are made of steel and may be equipped with a ceramic tip for longer life. After the coating is applied, it passes through a dryer, usually an IR dryer, a hot air dryer, or a cylinder dryer.

The grammage of the ductile pre-coated cellulose-based substrate may be, in one embodiment, from 40 to 80 g/m2, such as from 2 to 75 g/m40, such as from 2 to 70 g/m40, such as from 2 to 65 g/m40.

The thickness of the ductile pre-coated cellulose-based substrate may be 35 to 70 gm, such as 35 to 65 gm, such as 40 to 60 gm, such as 45 to 60 gm.

The first top side of the ductile pre-coated cellulose-based substrate can have very low porosity.

Ductile basecoat precoat may be applied as an aqueous latex composition having a solids content of 48 to 51% by weight and a Brookfield viscosity of 100 to 1000 mPa.s, a pH of 5.5 to 8.

The ductile base coat precoat may also be applied as an aqueous composition by means of knife or rod coating, in an amount of 5 to 15 g/m2, on a dry weight basis.

The thus obtained dried and pre-coated cellulose-based substrate may be subsequently supercalendered, such as at a calender nip pressure of at least 100 kN, such as at least 200 kN, such as 300 kN or higher, and at a heat roll surface temperature of 100 to 300 °C, such as 100 to 240 °C, such as 150 to 240 °C. The cellulose-based substrate including the ductile base coat precoat may be calendered to obtain an air permeability value of less than 100 nm/(Pa.s), which is the lower limit of the range within which the ISO 5636-5:2013 test method is applicable, and further an air permeability value of less than 1 nm, such as from 40 to 900 pm/(Pa.s), such as from 40 to 800 pm/(Pa.s), such as from 100 to 700 pm/(Pa.s), such as from 200 to 500 pm/(Pa.s), as determined by the SCAN-P 26:78 test method. It is believed that the remarkably dense surface obtained by the ductile pre-coating base layer of the high-density cellulose-based substrate further promotes the robustness effect of the gas barrier properties beyond what has been seen so far when subsequently coated with thin gas barrier layers.

The ductile pre-coated cellulose-based substrate may have a surface roughness of the first upper side of less than 100 ml/min Bendtsen, such as less than 80 ml/min Bendtsen, such as less than 50, such as less than 30, such as less than 20 ml/min Bendtsen, as measured in accordance with SS-ISO8791-2:2013.

A different measure of surface roughness is the Parker Print Surface Roughness (PPS), measured according to TAPPI standard 555 om-15, which is the same as ISO standard 8791-4.

The PPS roughness of the first surface of the ductile pre-coated cellulose-based substrate on the upper side is preferably less than 3.0 pm, such as less than 2.8 pm, such as less than 2.5 pm, such as less than 2.2 pm, such as less than 2.0 pm, such as 1.8 pm or less, for further improved gas barrier coating performance, as determined by the above test method.

The cellulose-based substrate including the ductile basecoat precoat as well as the at least one gas barrier coating may have a PPS surface roughness of less than 3.0 pm, such as less than 2.8 pm, such as less than 2.5 pm, such as less than 2.2 pm, such as less than 2.0 pm, such as 1.8 pm or less, as measured in accordance with TAPPI standard 555 om-15, which is the same as ISO standard 8791-44.

The density of the ductile precoated cellulose-based substrate may be greater than 900 kg/m3, such as greater than 1000 kg/m3, such as greater than 1100 kg/m3, such as greater than 1200 kg/m3. The precoated cellulose-based substrate may be calendered, preferably supercalendered, to obtain high density and surface smoothness.

A lower surface roughness provides a perfect interface for subsequently applied adjacent layers and coatings, with a reduced number of imperfections such as pores and unevenness in the coating layer. Consequently, the additional coating or layer can be applied at a higher grade, at a lower thickness, or both. For the same coating thickness of a gas barrier coating, this results in improved oxygen barrier properties for the coating itself.

The pre-coated cellulose-based substrate, including the ductile base coat precoat, may have a density of at least 950 kg/m3, such as at least 1000 kg/m3, such as at least 1100 kg/m3, measured in accordance with ISO 534:2011, and a grammage of 35 to 75 g/m2, such as 2 to 75 g/m40, such as 2 to 70 g/m45, such as 2 to 65 g/m45.

The application of the ductile base layer precoat, together with the calendering process of the thus coated cellulose-based substrate, provides a gain in ductility of the precoated cellulose-based substrate and consequently also in the final gas barrier coated material, which will result in improved gas barrier properties also in laminated packaging materials, such that the properties are more resistant to breakage, cracking and damage in the process of converting into a package as well as in the handling and distribution of the package.

Increased ductility reduces the material's tendency to crack in paper and therefore also reduces the tendency for gas barrier coatings to crack, thanks to a redistribution of stress and elongation over a larger surface area, for example, during folding operations.

The at least one gas barrier coating, which provides the barrier-coated cellulose-based substrate of the invention with its basic gas barrier properties, is a gas barrier dispersion coating, applied by means of dispersion or solution coating, and a barrier deposition coating, applied by means of a vapor deposition method.

Gas barrier coatings applied by dispersion coating or in aqueous solution of gas barrier compositions may comprise polymers that have inherent gas barrier properties and are food-safe and environmentally sustainable both in terms of recyclability and in industrial coating and lamination processes. Such polymers are therefore water-dispersible and/or water-soluble and can be applied by an aqueous "dispersion coating" process or a process known as "liquid film coating." Non-aqueous or only partially aqueous coating compositions, such as those based on alcohols or mixtures of alcohol and water, could also be suitable to achieve the good results of the present invention. They would, however, likely be less suitable from the perspective of environmental sustainability than purely water-based coating compositions.

In one embodiment, the barrier dispersion coating comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH), starch, starch derivatives, xylan, xylan derivatives, nanofibrillar cellulose/microfibrillar cellulose (NFC/MFC), and mixtures of two or more thereof.

The barrier dispersion coating is applied by means of dispersion or solution coating in a total amount of 0.2 to 5 g/m2, such as 2 to 5 g/m0.5, such as 2 to 4 g/m0.5, such as 0.5 to 3.5 g/m2, such as 1 to 3.5 g/m2, such as 1 to 3 g/m2, by dry weight.

Suitable processes for coating low dry content gas barrier polymer dispersion/solution compositions are, in general, any suitable wet coating method, such as gravure roll coating, smooth roll coating, reverse roll coating, wire rod coating, knife coating, lip coating, air knife coating, and curtain flow coating. The experiments of the present invention were carried out by means of smooth roll coating, but it is believed that any of the above or other liquid film coating methods which would contribute to generating a homogeneous layer having a smooth and uniform coated surface would be suitable for providing gas barrier coatings in accordance with the invention.

In a more specific embodiment, the barrier dispersion coating compositions are based on the two most common types of polymers and copolymers suitable for dispersion coating, based on vinyl alcohol monomers, i.e., polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH).

The gas barrier polymer can preferably be PVOH, because it provides good film-forming properties, gas barrier properties, cost-effectiveness, food compatibility, and odor barrier properties.

A PVOH-based gas barrier composition performs best when the PVOH has a degree of saponification of at least 98%, preferably at least 99%, although PVOH with lower degrees of saponification will also provide oxygen barrier properties.

On the other hand, EVOH can be advantageous in providing some moisture resistance to the barrier material, since the copolymer comprises ethylene monomer units. The amount of ethylene monomer units depends on the choice of EVOH grade, but their presence will be at the expense of some oxygen barrier properties, compared to neat PVOH. Conventional EVOH polymers are typically intended for extrusion and cannot be dispersed or dissolved in an aqueous medium to produce a thin liquid film-coated barrier film of 3.5 g/m2 or less. It is believed that EVOH must comprise a fairly high amount of vinyl alcohol monomer units to be water-dispersible and that the properties should be as close as possible to those of liquid film coating grades of PVOH. Therefore, an extruded EVOH layer is not an alternative to a liquid film coated EVOH, because it inherently has less PVOH-like properties than extrusion coating EVOH grades, and because it cannot be applied in a cost-effective quantity below 5 g/m2 as a single layer by extrusion coating or extrusion lamination.

Nanocrystalline cellulose, NCC, is a form of nanocellulose but is not the same as "microfibrillar cellulose", "MFC" (CMF) or "nanofibrillar cellulose", "NFC (CNF)".

Therefore, MFC/NFC may contain longer particles, so-called "fibrils" that have a width of 10-1000 nm and a length of at least 1 gm, such as up to 10 gm, such as up to 100 gm.

Both MFC and NFC have an aspect ratio of 50 or higher, while NCC/CNC can be defined as having an aspect ratio lower than 50, for example, according to ISO/TS 20477:2017 and TAPPI WI3021 draft standard.

The term "NCC" is used for shorter particles and "rod-like" particles, which have a width of 3 to 100 nm and a length of 100 to more than 1000 nm, such as 100 to 3000 nm, such as 100 to 1000 nm, such as 100 to 500 nm. The majority of the NCC particles in the composition should have this dimension, it can be 100 to 500 nm in length, such as 100 to 200 nm and with a small width of 3 to 100 nm.

The barrier dispersion coating composition may further comprise from about 1 to about 20% by weight of the inorganic layered compound based on the dry weight of the coating, such as exfoliated nanoclay particles, such as bentonite. Thus, the barrier layer may include from about 99 to about 80% by weight of the polymer based on the weight of the dry coating. An additive, such as a dispersion stabilizer, antifoam, or the like, may also be included in the gas barrier composition, preferably in an amount of no more than 1% by weight based on the dry coating. The total dry content of the composition is preferably from 5 to 20% by weight, such as from 7 to 15% by weight.

A further possible additive in the barrier precoat composition may be a carboxylic acid-functional polymer or compound, in order to improve the water vapor and oxygen barrier properties of a PVOH coating. Suitably, said carboxylic acid-functional polymer is selected from ethylene acrylic acid copolymer (EAA) and ethylene methacrylic acid copolymers (EMAA), or mixtures thereof. In one embodiment, such a barrier layer mixture may consist essentially of PVOH, EAA, and an inorganic layer compound. The EAA copolymer may be included in the barrier layer in an amount of about 1-20% by weight, based on the weight of the dry coating.

It is believed that some further improved oxygen and water barrier properties may result from an esterification reaction between PVOH and EAA at a higher drying temperature, whereby the PVOH becomes crosslinked by hydrophobic EAA polymer chains, which are thus incorporated into the PVOH structure. Crosslinking can alternatively be induced by the presence of polyvalent compounds, for example, metallic compounds such as metal oxides. Such mixtures are, however, more expensive due to the cost of additives and may be less preferred from a recyclability standpoint.

Therefore, although it is more preferable to use a barrier dispersion coating from a pure PVOH or EVOH composition, advantageous gas barrier results can also be obtained with barrier dispersion coatings comprising additional additives as described above.

Therefore, the barrier dispersion coating may be applied in a total amount of 0.2 to 5 g/m2, such as 0.2 to 4 g/m2, more preferably 0.5 to 4 g/m2, such as 0.5 to 3.5 g/m2, such as 1 to 3 g/m2, by dry weight. Below 0.2 g/m2, no gas barrier properties will be achieved at all, while above 3.5 g/m2, the coating may make the packaging laminate unprofitable, due to the high cost of barrier polymers in general and the high energy cost of evaporating the liquid. A recognizable level of oxygen barrier can be achieved by PVOH at 0.5 g/m2 and above, and a good balance between barrier properties and cost is typically achieved between 0.5 and 3.5 g/m2.

In one embodiment, the barrier dispersion coating may be applied in two or even three consecutive steps with intermediate drying, as partial layers. When applied as two partial layers or "partial coatings," each layer is suitably applied in amounts of 0.2 to 2.5 g/m2, preferably 0.5 to 1.5 g/m2, and allows for a higher quality overall layer from a smaller amount of gas-liquid barrier composition. More preferably, the two partial layers may be applied in an amount of 0.5 to 1.5 g/m2 each.

By the unexpected improvement of the invention, the barrier dispersion coating will therefore not be applied directly onto the paper or cellulose-based substrate, but will be preceded by a first ductile basecoat precoat of a polymer and material composition different from the composition of the gas barrier material, to prepare the substrate surface for application of the gas barrier coating. It is believed that the particular properties of the aqueous ductile basecoat precoat composition promote a dense and uniform top basecoat surface for further gas barrier coating and compatible adhesion and wettability chemistry for subsequent application of, for example, a polyvinyl alcohol-based gas barrier coating. The primary improving effect, however, is that the first ductile basecoat precoat has the ability to absorb stress and elongation on the barrier-coated cellulose-based substrate as it is folded and abused, when used in a laminated packaging material.

The barrier-coated cellulose-based substrate has on its first upper surface a first coating of a gas barrier material formed by coating and then drying a dispersion or solution of an aqueous gas barrier composition, and further a vapor deposition coating of a gas barrier material, as selected from metals, metal oxides, inorganic oxides, and diamond-like amorphous carbon, applied over the first barrier dispersion coating.

Therefore, the barrier-coated cellulose-based substrate can be coated with a gas barrier material by vapor deposition coating on its upper surface at a thickness of 2 to 80 nm, such as 2 to 50 nm, such as 2 to 45 nm.

The vapor-deposited barrier coating that will ultimately be applied to the top surface of the cellulose-based substrate is applied by means of physical vapor deposition (PVD) or chemical vapor deposition (CVD), for example, plasma-enhanced chemical vapor deposition (PECVD).

In general, below 5 nm, the barrier properties may be too low to be useful and above 200 nm, such as above 100 nm, such as above 50 nm, depending on the type of vapor deposition coating, the barrier coating may be less flexible and therefore more prone to cracking when applied over a flexible substrate and would also cost more.

Other examples of vapor deposition coatings include aluminum oxide (AlOx, Al2O3) and silicon oxide (SiOx) coatings. In general, these PVD coatings are more brittle and less suitable for incorporation into packaging materials by lamination, while metallized layers, as an exception, have mechanical properties suitable for lamination materials despite being PVD coated.

Typically, a metallized layer of aluminum inherently has a thin surface portion consisting of an aluminum oxide due to the nature of the metallization coating process used.

In one embodiment, such a metallized aluminum layer has been applied at an optical density (OD) of 1.8 to 2.5, preferably 1.9 to 2.2. At an optical density below 1.8, the barrier properties of the metallized film may be too low. Above 2.5, on the other hand, the metallization layer may become brittle, and the thermostability during the metallization process will be low due to the higher heat load when metallizing the substrate film for a longer period of time. The quality and adhesion of the coating may be adversely affected.

Other coatings can be applied using a plasma-enhanced chemical vapor deposition (PECVD) method, in which a compound vapor is deposited onto the substrate under more or less oxidizing conditions. Silicon oxide (SiOx) coatings can also be applied, for example, using a PECVD process, and very good barrier properties can then be achieved under certain coating conditions and gas recipes.

DLC defines a class of amorphous carbon (diamond-like carbon) materials that exhibit some of the typical properties of diamond. Preferably, a hydrocarbon gas, such as, for example, acetylene or methane, is used as the process gas in a plasma to produce a barrier layer coating of amorphous hydrogenated carbon applied by a vacuum PECVD process, i.e., a DLC. DLC coatings applied by vacuum PECVD provide good adhesion to adjacent polymer or adhesive layers subsequently laminated into a laminated packaging material. Particularly good adhesion to adjacent polymer layers is obtained with polyolefins, and in particular polyethylene and polyethylene-based copolymers.

The at least one gas barrier coating comprises a barrier dispersion coating, first applied by means of dispersion or solution coating onto the ductile base layer, pre-coating and a barrier deposition coating, subsequently applied by means of a vapor deposition method, onto the barrier dispersion coating.

A barrier-coated cellulose-based substrate may also be provided, further comprising a ductile base layer coating also applied to the back side of the substrate. Such an additional ductile coating on the other side of the cellulose-based substrate ensures optimal performance against increased abuse and creasing of a laminated packaging material comprising the barrier-coated cellulose-based substrate, so that improved oxygen barrier properties of the ultimately formed and filled packaging containers are achieved.

Therefore, the back side of the substrate may also optionally be coated with at least one gas barrier coating of at least one gas barrier material as defined in any of the above embodiments.

The gas barrier coated cellulose-based substrate obtained by the above method therefore provides excellent low TTO and low TTVA also after lamination in a laminated packaging material and furthermore after the folding and sealing operations of such a laminated material in packaging.

A laminated paperboard-based packaging material for packaging oxygen-sensitive products may comprise a main paper or paperboard layer, a first, outermost, liquid-impermeable layer of material, a second, innermost, liquid-impermeable layer of material, and, disposed on the inner side of the main paper or paperboard layer, towards the interior of a packaging container made from the packaging material, between the main layer and the second, innermost layer, the barrier-coated cellulose-based substrate of the invention.

A main layer of paper or board may have a thickness of about 100 gm to about 600 gm, and a surface weight of about 100-500 g/m2, preferably about 200-300 g/m2 and may be a conventional paper or board of suitable packaging quality.

For low-cost, long-term aseptic packaging of liquid foods, a thinner packaging laminate may be used, having a thinner paper core layer. Packaging containers made from such packaging laminates are not pleated and are more similar to pillow-shaped, flexible pouches. A suitable paper for such pouch-type packages typically has a surface weight of about 50 to about 140 g/m2, preferably about 70 to about 120 g/m2, more preferably about 70 to about 110 g/m2. Since the barrier-coated substrate in the present invention may itself contribute some stability to the laminate, the paper layer corresponding to a "core" layer may be even thinner and interact with the cellulose-based barrier substrate in an interleaved interaction to produce a laminated packaging material having all of the desired mechanical properties.

The barrier-coated cellulose-based or paper-based substrate may be bonded to the main layer by an intermediate adhesive or a thermoplastic polymer tie layer, thereby bonding the uncoated surface of the barrier-coated paper to the main layer. The tie layer may be a polyolefin layer, such as, in particular, a layer of a polyolefin copolymer or blend, such as one comprising ethylene monomer units in the majority. The tie layer may bond the main layer to the barrier-coated cellulose-based substrate by melt extrusion lamination of the molten tie polymer as a layer between the webs and simultaneously pressing the three layers together, while being sent through a laminating roll nip under simultaneous cooling, thereby providing a laminated structure by extrusion lamination. Melt extrusion lamination requires a sufficient amount of molten polymer, in this case typically a polyolefin, such as low-density polyethylene, to bond the two cooler surfaces together. A sufficient amount is usually 12 to 20 g/m2, possibly 12 to 15 g/m2.

Other suitable bonding or tie layers within the laminate material, such as for example between the main or core layer and the barrier coated cellulose based substrate, or between the innermost heat-sealable liquid impermeable layer and the barrier coated paper substrate, may also be referred to as adhesive thermoplastic polymers, such as modified polyolefins, which are mainly based on LDPE or LLDPE copolymers or graft copolymers with monomer units containing functional groups, such as carboxylic or glycidyl functional groups, for example (meth)acrylic acid monomers or maleic anhydride (MAH) monomers, (i.e. ethylene-acrylic acid copolymer (EAA) or ethylene-methacrylic acid copolymer (EMAA)), ethylene-glycidyl(meth)acrylate copolymer (EG(M)A) or MAH-grafted polyethylene (MAH-g-PE). Another example of such modified polymers or adhesive polymers are the so-called ionomers or ionomer polymers. Preferably, the modified polyolefin is an ethylene-acrylic acid copolymer (EAA) or an ethylene-methacrylic acid copolymer (EMAA).

The barrier-coated cellulose-based substrate may be bonded to the main ply by wet-applying an aqueous dispersion of an adhesive composition comprising an adhesive polymer binder to one of the surfaces of the web to be laminated and pressing the two paper webs together as they are advanced across a nip of a laminating roll, thereby providing a laminated structure by wet lamination. The moisture in the aqueous adhesive composition is absorbed into the fibrous cellulose network of the two paper plies and partially evaporates over time during subsequent lamination processes. Therefore, a forced drying step would not be necessary. The barrier-coated cellulose-based substrate may therefore be laminated to the main layer of 0.5 to 6 g/m2, such as 1 to 5 g/m2, such as 1 to 5 g/m2, by dry weight, of an interjacent binding composition comprising a binder selected from the group consisting of acrylic polymers and copolymers, starch, starch derivatives, cellulose derivatives, vinyl acetate polymers and copolymers, vinyl alcohol polymers and copolymers, styrene-acrylic latex or styrene-butadiene latex copolymers or bio-latex adhesives. In order to obtain the best possible environmental and sustainability profile, adhesive binders that are derived from plants or non-fossil sources are preferred.

Such a low quantity of an interjacent bonding composition can only be applied by dispersion coating or in aqueous solution of a polymer binder, and its application by extrusion coating or extrusion lamination of a single-layer polymer melt is not possible due to the nature of the melt-layer extrusion process. Since the surfaces of the layers to be bonded are both made of cellulose, such wet lamination is carried out by absorption of the aqueous medium into the respective cellulose layers, and thus a thin, dry bonding layer can be formed at the interface between the two layers.

Suitable materials for the outermost and innermost liquid-impermeable layers may be thermoplastic polymers, such as polyolefins such as polyethylene and homo- or copolymers of polypropylene, preferably polyethylenes and more preferably polyethylenes selected from the group consisting of low-density polyethylene (LDPE), linear LDPE (LLDPE), single-site catalyst metallocene polyethylenes (m-LLDPE), and blends or copolymers thereof. Such thermoplastic polymers also have the advantage of being readily weldable, i.e., heat-sealable, to the same or similar polymers and to other materials with thermoplastic behavior. According to one embodiment, the outermost, liquid-impermeable, heat-sealable layer may be an LDPE, while the innermost, heat-sealable, liquid-impermeable layer may be a blend composition of m-LLDPE and LDPE to obtain optimal lamination and heat-sealing properties.

The outermost layer may simply be protective against liquids and dirt, such that any sealing of the outer surface to another surface or element, such as an opening device or the like, will be achieved by means of an additional glue or hot melt. For the packaging of products with lower requirements regarding seal strength and impermeability, this also applies to the second, innermost layer. For the packaging of fluid, semi-liquid, or viscous products and moist foods, the qualities of the packaging container depend more on the second, innermost layer also being heat-sealable to produce strong, impermeable packages that can transport the filled product under all handling and distribution circumstances. Therefore, the second, innermost layer may be required to be both liquid-impermeable and heat-sealable.

The same thermoplastic materials, as listed with respect to the outermost and innermost layers, such as polyolefins and, in particular, polyethylene-based materials, may also be suitable for bonding layers within the laminate, i.e., between a primary or core layer, such as paper or paperboard, and the barrier-coated cellulose substrate. Thus, the thermoplastic bonding layer may be a polyethylene layer, such as a low-density polyethylene (LDPE) layer.

The second, innermost, liquid-impermeable, heat-sealable polyolefin layer may be a prefabricated film comprising the same or similar polyolefins as described above, to enhance the robustness of the mechanical properties of the packaging material. Due to the manufacturing process in film blow-casting operations, and the optional subsequent film orientation operation steps, the polymers of such films acquire different properties than are possible from coated polyolefin layers simply by (co)extrusion. Therefore, such a prefabricated polymer film can contribute to the mechanical robustness of a laminated packaging material and to the mechanical strength, package integrity, and further reduced loss of barrier properties of packaging containers formed and filled with the laminated packaging material.

A laminated packaging material may have a prefabricated polymer film laminated between the barrier-coated cellulose-based substrate and the innermost liquid-impermeable second layer of material to enhance the robustness of the laminated packaging material's mechanical properties. A prefabricated film has a higher degree of orientation of the polymer from which it is made and therefore has different mechanical properties than a layer simply extrusion-coated or extrusion-laminated of the same or corresponding polymer. Therefore, by incorporating such a film into the structure, the overall laminated material can be made stronger and more resistant to the harsh subsequent processing of the material. Such prefabricated films can be avoided in the material, as they add costs both from the perspective of material sourcing and the lamination operation. Prefabricated films can have different mechanical properties and can range from biaxially oriented tough films obtained by simple extrusion of cast films to films manufactured by blown film with the inherent polymeric orientation produced in that process, or with additional subsequent orientation. Alternatively, polymeric materials that are simply extrusion coated or laminated can be used.

The second, innermost layer of a heat-sealable, liquid-impermeable material can be a polyolefin, preferably a blend of low-density polyethylene, LDPE, and metallocene-catalyzed linear low-density polyethylene (using a single-site or constrained-geometry catalyst), m-LLDPE. This is the most commonly used polymer type today for the innermost layer, achieving the best balanced liquid-impermeability and heat-sealability properties, and generating the best possible package integrity for heat-sealed packaging containers. By carefully choosing the composition of this layer, the amount of polymer in this layer can be optimized to be as low as possible while still producing strong, reliable product-filled containers.

The second innermost heat-sealable liquid-impermeable layer of material may be, or comprise, a prefabricated polymer film, comprising a heat-sealable thermoplastic polymeric material and, optionally, an additional layer of a material to provide improved robustness of the mechanical properties of the laminated packaging material.

The purpose of any one of the specific examples of laminates listed above is to add complementary properties to the laminated packaging material, when only the barrier-coated cellulose-based substrate is used as a gas barrier material in the laminated structure, or where the applied coating provides only some gas barrier properties, or where the coating only has moisture-sensitive gas barrier materials. By laminating the barrier-coated cellulose-based substrate to an additional polymer film, which can add moisture resistance or additional water vapor barrier properties, the at least two different barrier materials can interact to provide additional enhanced overall barrier properties to the overall laminate structure. Typical examples of such prefabricated films, adding at least water vapor barrier properties, can be metallized films and polymer films that include fillers, such as mineral fillers in the form of flakes or other small particles, that help retard the diffusion of water vapor through the laminated structure. The necessary bonding layer between the barrier-coated cellulose-based substrate and the additional barrier film can ensure such enhanced barrier properties, since the interjacent bonding layer acts as a "cushion" and also as a "gas or vapor migration interface" in the laminate structure.

The outermost and innermost liquid-impermeable layers, and the lamination layers within the laminate structure, typically and inherently do not provide high barrier properties to migrating gas molecules or small molecules. Their purpose is to provide a direct barrier to liquid water penetrating the cellulose-based core material and other paper layers. Liquid barrier layers also prevent water vapor from migrating into the cellulose to the point of wetting, but they are not able to maintain the moisture content of the laminated structure at zero or at the low level of "dry" paper (which is approximately 7-8% in a room temperature environment, i.e., 23 degrees C and 50% relative humidity (RH). The moisture content in the laminated board material of a liquid-filled packaging container is usually quite high, and migration through the material will occur unless an additional water vapor barrier is included, such as an aluminum foil, a vapor-deposited metallization layer, another vapor deposition coating, a layer of inorganic material, or another layer of polymeric material.

A laminated packaging material as described above can provide good integrity when formed into filled packaging containers, through good adhesion between adjacent layers within the laminated construction and by providing good quality of the barrier coatings and the ductile base layer precoat, both individually and in combination. Particularly for the packaging of liquids and moist foods, it is important that the interlayer adhesion within the laminated packaging material, as well as the oxygen gas barrier properties, be maintained even under moist packaging conditions.

A packaging container formed from a described laminated packaging material can be partially sealed, filled with liquid or semi-liquid food and subsequently sealed, by sealing the packaging material onto itself, optionally in combination with a plastic opening or top of the package.

In conclusion, robust and reliable packages for packaging liquid foods with long-term shelf life and storage can be obtained using the barrier-coated cellulose-based substrate and the laminated packaging material comprising it, as defined by the invention, thanks to the overall improved barrier properties, which are maintained even during folding of the packaging material. The structure of the laminated packaging material works better for forming folded-shaped packages, both with regard to the good adhesion between the barrier-coated substrate and the other layers of the laminate and with regard to the improved contribution to the gas barrier properties of the barrier-coated substrate itself. The latter is likely due to greater flexibility and resistance to tension and deformation, thanks to the ductile base layer pre-coating on the barrier-coated cellulose-based substrate. It has been observed that the ductile pre-coating can prevent the barrier coating and the innermost liquid-impermeable layers from elongating to an extent that results in cracking. The ductile precoating most likely redistributes the high local stress and elongation in the cellulose-based substrate, the barrier coating, and the innermost liquid-impermeable layers during bending. The elongation level then becomes lower and is distributed over a larger area.

Examples and description of preferred embodiments

Preferred embodiments of the invention will now be described with reference to the drawings, in which:

Fig. 1a shows schematically in cross-section embodiments of cellulose-based substrates with barrier coating according to the invention,

Fig. 2a shows a schematic, cross-sectional view of an example of a laminated packaging material, comprising the barrier-coated cellulose-based substrate of Fig. 1a,

Fig. 3a schematically shows a method for dispersion coating a base coat or a barrier precoat composition onto a cellulose-based substrate,

Fig. 3b schematically shows a method, for melt (co)extrusion coating one or more layers of a liquid-impermeable and heat-sealable thermoplastic polymer onto a web substrate, to form the innermost and outermost layers of a packaging laminate of the invention,

Fig. 4a shows a schematic view of a plant for physical vapor deposition (PVD) coating, using a solid metal evaporation piece, on a substrate film,

Fig. 4b shows a schematic view of a plant for plasma-enhanced chemical vapor deposition (PECVD) coating, by means of a magnetron plasma, on a substrate film,

Fig. 5a, 5b, 5c and 5d show typical examples of packaging containers produced from a laminated packaging material comprising a cellulose-based substrate with barrier coating according to the invention,

Fig. 6 shows the principle of how such packaging containers are manufactured from the packaging laminate in a continuous, roll-fed, form-fill-seal process,

Fig. 7 is a diagram showing the effect of surface roughness on the oxygen transmission rate of different paper substrates, and

Fig. 8 shows a schematic cross-sectional view of an embodiment of a cellulose-based substrate pre-coated with a ductile base layer.

Examples

Example 1

The paper property characteristics were evaluated on a laboratory scale to provide the most suitable cellulose-based substrate for the present invention.

Table 1 below shows the main properties used to select the most suitable paper substrate. Various paper structures were tested with respect to their porosity (represented by Gurley air resistance), their mechanical strength characteristics (represented by elongation and tensile energy absorption-TEA), and their surface smoothness (represented by Bendtsen and PPS roughness values). The porosity of a paper can be measured as air resistance with the unit s/(100 ml) determined using the Tappi T460 om-02 standard, or as air permeability with the unit gm/(Pa s), as determined by the ISO5036-5:2013 standard. For papers with very low porosity, the air permeability, with the unit gm/(Pa s), nm/(Pas), or pm/(Pas), is determined using the SCAN-P 26:78 standard.

Among the papers analyzed, the structures that presented the lowest porosity, with the highest Gurley air resistance value, sometimes not even detectable by the equipment due to an excessively high value, were papers 1, 2 and 11.

Table 1: Paper substrates evaluated with different porosity, mechanical strength and surface roughness properties

(*) Properties that due to their high value exceeded the detection limit of the equipment.

GPP stands for greaseproof paper, CP stands for pre-coated paper, and NC stands for uncoated paper.

The most suitable combination of the evaluated paper properties was found to be that described in K in Table 1 above. To confirm that the structure was the most suitable for gas barrier application, the base layer precoat and gas barrier coating formulations were applied to validate the oxygen transmission levels achieved with the selected paper base. The ductile base layer precoat and barrier coatings were applied to the felt side, i.e., the top side, of the papers.

Table 2 shows a summary of the analyses performed on coated papers. The surface roughness of the precoated papers was evaluated in PPS. The effect of the base coat precoat on paper roughness represents the change (in %) in roughness, measured for coated papers, compared to the roughness measured for uncoated papers.

The paper substrates (A, B, F, G, and K) were further coated with one or two layers of a nanocrystalline cellulose (NCC) gas barrier solution (total wet thickness of ~25 pm). The coatings were evaluated for coating weight, roughness, kit oil, grease resistance, and oxygen barrier. Evaluation of these barrier coating properties indicates the effects of the base paper sheet type and its initial roughness on the subsequent gas barrier coating performance.

The kit oils were evaluated according to Tappi standard T559 pm96 (KIT test). In this test, the organic solvent mixture is dripped onto the surface of the coated papers, followed by inspection to determine whether the organic solvents have penetrated the barrier layer and are absorbed by the paper. For this evaluation, KIT test mixtures of grades 7-12 were used.

The oxygen barrier properties for Table 2 were evaluated according to ASTM D3985 and F1927-50 using a MOCON Ox-T ran Model 2/22 sensor instrument. Measurements were taken at 23°C and 70% relative humidity at 101.32 kPa (1 atm), i.e., 100% oxygen. For papers with higher initial surface roughness, the OTO was measured after two coating coats (because one coat failed to form a good barrier). For papers with low surface roughness, samples with one coating coat were evaluated (due to good barrier formation).

Table 2: Summary of the analyses performed for the coated papers selected for barrier application

The effect of roughness on the oxygen transmission rate of barrier-coated papers is shown in Figure 7.

As shown in Table 2 and as observed, the surface roughness of the substrate paper has a substantial effect on the final barrier performance after coating. First, the higher the surface roughness of the base paper, the higher the weight of applied gas barrier coating required, although even when wet, higher thicknesses were applied to the different papers. This can be observed for papers A and B, which have relatively high surface roughness and consequently require high gas barrier coating weights. Furthermore, for papers with higher roughness measurements, typically >3 pm (PPS) as observed for A and B, the NCC barrier coating solution reduced the paper roughness. For papers with low surface roughness, there is a slight increase in roughness, but in terms of pm, the roughness remains very low.

Second, as can be seen in Table 2 and Figure 7, the lower the roughness of the base paper (typically < 3 µm), the better the barrier performance after barrier application. For paper structures such as G and K, with low roughness, it can be seen that only one coating layer was sufficient to achieve excellent oxygen and grease barriers, whereas for papers A and B, an insufficient oxygen barrier was achieved, even though a high coating weight was applied. This implies that not only is the barrier performance improved, but also the number of layers required to form the barrier is reduced. After testing the grease resistance of the papers, all papers demonstrated an excellent grease barrier (KIT 12). Likewise, all papers, except paper F, demonstrated grease resistance after paper creasing. It appears that paper roughness has a smaller effect on the grease barrier compared to the oxygen barrier.

The performance of Paper F differed from that of the other papers tested. With low roughness, Paper F showed insufficient barrier performance in terms of oxygen transmission and grease resistance. Based on the properties of Paper K, combining low surface roughness with low porosity and providing good oxygen barrier properties, it can be concluded that not only roughness affects barrier performance, but also the composition of the paper, i.e., its porosity, and the composition of its surface.

The surface roughness of the paper is a very important parameter that will affect the effectiveness of the applied barrier layer, in terms of the number of layers applied, the weight of the coating applied, and the barrier performance. A PPS roughness value of less than 3 pm is required to achieve a single-layer coating and achieve good barrier performance. Surface roughness is not the only important parameter to consider, as the composition and strength properties of each paper can also affect performance.

Therefore, after studying and evaluating all the paper substrate structures described above and considering the combination of air resistance properties of paper, i.e., porosity, surface roughness and paper performance in barrier tests after its application on paper, the paper structure named K was chosen as the most suitable structure to continue scale-up studies and design a proof of concept for barrier performance validation.

K paper is pre-coated and supercalendered, having a density greater than 1100 kg/m3 and is produced from 100% softwood Kraft pulp.

Example 2

The pre-coated high-density paper K is pre-coated on both sides, has a grammage of 55 g/m2, and its entire contents are repulpable. Figure 8 represents the structure of the pre-coated thin paper K, determined to be the best combination to ensure the performance of other gas barrier coatings applied to its top surface. The structure shown in Figure 8 has ductile coatings applied to both the top and bottom surfaces of the paper, which will be described below. These ductile basecoat coatings allow an optimal combination of low porosity and roughness to achieve the expected oxygen barrier performance. The ductile basecoat precoat is applied directly onto the paper fibers. Directly above the heavier layer on the top (or felt) side of the paper (B in Figure 8), the gas barrier coating must be applied at a later stage.

The fiber composition represented as A in Figure 8 is formed solely from cellulose pulp fibers. These fibers are bleached kraft softwood fibers and can have a grammage of 30 to 50 g/m2. The coated paper grammage will then be 40 to 65 g/m2. The base paper for K paper has an uncoated grammage of 35 g/m2 and a ductile pre-coated grammage of 55 g/m2.

The upper and lower surfaces of the fibrous composition A were therefore coated with aqueous precoatings of ductile dispersion compositions. These coatings had a pH of 5.5 to 8, a solids content of 48 to 51%, a Brookfield viscosity of 100 to 1000 mPa.s, while the coated material exhibits a Tv ranging from -30 to 0 and from 0 to 30 (°C), and can be described in terms of chemical composition as an aqueous dispersion of a styrene-butadiene binder copolymer, a so-called SB latex and a kaolin clay filler. The precoating composition used comprised about 15% by weight of SB latex, about 80% by weight of kaolin filler, about 4% by weight of crosslinked starch compound and further additives, such as less than 2% by weight of a thickening agent.

As illustrated in Figure 8, the coating layer B applied to the top side of the paper may have a weight of 5 to 15 g/m2, such as 10 to 15 g/m2, applied in the form of a single layer. The coating composition illustrated in C, applied to the bottom/back side of the paper, may have a grammage of 1 to 10 g/m2 applied in a single layer and is also obtained from an aqueous dispersion comprising a styrene-butadiene copolymer and kaolin. The coated paper as illustrated in the set of A, B and C may therefore have a final grammage comprised between 40-65 g/m2.

The thus pre-coated K paper as illustrated in Figure 8, with layers A, B and C had a basis weight of 55 g/m2 and a final porosity of less than 100 nm/(Pa s) as determined by ISO5636-5:2013, which is the lower limit of the applicable range of the test method, and further less than 1 nm, as determined by SCAN-P 26:78. The pre-coated paper had a PPS roughness of less than 2 gm, i.e. about 1.8 gm, on its top side. The final NCC gas coated K paper according to Table 2 had a felt side surface roughness of about 2.8. Therefore, the pre-coated and barrier coated paper of the invention may have a PPS surface roughness of less than 3 gm, such as from 0.5 to 3 gm.

Example 3

The mechanical strength properties of the pre-coated cellulose-based substrates used were explored to demonstrate the importance and contribution of each layer of the pre-coated paper composition to the final application of the barrier-coated substrates.

Material failure due to crack nucleation and propagation in the substrate will create openings and discontinuities in the barrier coating layer, thereby destroying the barrier of the final package. The greater the elongation the substrate can experience before failure, the more resistant it will be to various loads, such as bending during package formation. By becoming more flexible, the structure after precoating with a ductile material and subsequent drying and calendering allows the precoated paper structure to more effectively resist bending and the initiation of surface cracks.

This reduced stiffness of the structure containing cellulose fibers and the top and bottom coatings after calendering can be illustrated by the reduction in Young's modulus, as shown in Tables 3 and 4, in both the DF and DT directions of the paper. The reduction in Young's modulus means that the stiffness of the overall structure of the material decreases, allowing the material to gain greater flexibility and therefore become more resistant and durable to creasing and folding processes.

The application of a flexible or ductile base layer precoat over the fibrous layer allows for a gain in ductility of the final material, which will result in a material that is more resistant to breakage, cracking, and damage during the packaging conversion process.

Table 3: Average of the values obtained for the tension x elongation curves of each pre-coated paper layer material described in Figure 7 (i.e. A B F G K), as well as the influence of the individual coating layers on the final ductility of each of the materials in the DF direction of the paper.

Table 4: Average of the values obtained for the stress x elongation curves of each pre-coated paper layer material described in Figure 7 (i.e., A B F G K), as well as the influence of the individual coating layers on the final ductility of the materials in the DT direction of the paper.

The mechanical strength properties of the precoated and uncoated papers evaluated in this case, when combined with the results of the laboratory barrier application exploration, provide insight into the excellent performance achieved. For example, elongation at maximum load increases as the cellulose-based substrate or paper is precoated (measurements "B") and further as the precoated paper is calendered (measurements "C"). This confirms the beneficial effect of providing a more ductile/flexible material as a substrate for the gas barrier, so that the gas barrier-coated substrate can withstand greater elongation without cracking during the conversion of the packaging material into packaging.

Example 4

The invention described herein, in addition to providing unique features that allow high levels of oxygen barrier to be achieved, is therefore a solution capable of replacing non-renewable components in packaging, has a high content of renewable materials and is 100% repulpable or recyclable in accordance with the PTS RH 021/97 standard.

To recycle the thin, ductile, pre-coated paper substrate selected for the application developed in this case, in addition to performing repulpability tests in accordance with the PTS RH 021/97 standard, a repulpability study was also carried out in the laboratory.

To evaluate repulpability in the laboratory, a paper sample of known weight was dispersed at 23°C using a device capable of 3000 rpm for 20 minutes of agitation. After the third minute of agitation, the paper was already repulpable. No lumps were detected in the water suspension, indicating that the paper was already dispersed in the water.

Example 5

An NCC-based gas barrier coating formulation was used to coat the flexible pre-coated paper substrate, which can be characterized as containing 5 to 22% solids and having a viscosity of 600 to 2500 ± 2 mPas. The chemical components of the formulation were based on NCC (CNC), PVOH, and starch-based materials and contained at least 50% renewable materials (NCC and starch), such as at least 50% NCC, and is 100% recyclable and biodegradable.

Nanocelluloses have problematic rheologies, so when added to blends with other polymers and components, they cause a change in rheology, altering the final viscosity of the suspension. NCCs (nanocrystalline cellulose or cellulose nanocrystals) are extracted from hardwood or softwood pulp, and all their dimensions are on the nanometer scale. The NCCs used have all their dimensions on the nanometer scale, with widths ranging from 5 to 20 nm and lengths from 150 to 400 nm.

A dual-layer gas barrier layer of nanocrystalline cellulose or PVOH or other gas barrier material can be formed on the top surface of the ductile precoated paper. A first gas barrier coating creates a gas barrier layer over the ductile base layer that precoats the top side of the paper, and a second gas barrier coating provides a second gas barrier layer over the first gas barrier coating layer.

The barrier layer application sequence is essential in this case, on the precoated ductile paper. The first gas barrier dispersion layer is applied over the ductile base layer precoat on the top surface of the paper by means of stick coating, and this layer is dried using infrared and hot air to form a homogeneous gas barrier layer on the surface. The application speed used in the tests was 300 to 600 m/min to ensure good quality of the gas barrier coating layers formed on the surface of the precoated ductile paper. The first gas barrier dispersion layer formed prepares the surface to receive the second barrier dispersion layer, which is also formed by means of stick coating, over the dried first barrier dispersion layer. The second applied gas barrier dispersion layer also undergoes a film-forming and drying process using infrared and hot air. It should be noted that the optimum range for hot air drying tested for formulation and ductile pre-coated paper is 90 to 150 °C.

Drying at the temperatures tested does not cause a loss of barrier levels and provides good coating film formation on the surface of the pre-coated paper, even at higher temperatures. Finally, to ensure proper winding and cooling of the barrier-coated paper substrate, after drying, the coated paper must be wound at temperatures below 40°C. This ensures the formation of a homogeneous film, guaranteeing high barrier performance against oxygen and grease.

Example 6

Various conditions for the large-scale application of a gas barrier coating to the surface of K paper, as described above, were tested. The gas barrier coating was applied on a pilot coating machine that allowed for the use of different technologies; however, bar and knife coating methods were the application technologies used to form the gas barrier coating layers applied over the ductile precoat B, as illustrated in Figure 8, with a total dry coating amount of 0.5 to 5 g/m2. The application bars are smooth and their diameters can vary; in this case, bar diameters of 18 to 30 mm were used. The tests were carried out by applying the gas barrier directly onto the ductile precoated base paper, as illustrated in Figure 8.

In a final prototype for proof of concept and scale-up, the characteristics of the ductile pre-coated papers used in the development were as described in Table 5 below.

Table 5: Characteristics of the paper used in a large-scale test

In this scale-up work, it was therefore observed that pre-coated paper substrates with lower surface roughness and lower porosity generally provided better results and improved oxygen barrier levels in formed and filled containers.

The NCC-containing barrier formulation was therefore applied over the ductile precoat B on the top side of the paper substrate A (Fig. 8), i.e. on the top surface with the highest precoat weight, forming a 2-layer gas barrier coating of 2 x 2.5 g/m2 NCC, resulting in a 21%O2 package TTO (cc/pkg/24 h) of 1.62 to 20.26 kPa (0.016 to 0.2 atm) and 50% RH, in accordance with ASTM F1307-14.

The aqueous dispersion containing cellulose nanocrystals was therefore applied to surface B in a first step, thereby consolidating a final gas barrier layer measuring approximately 2.5 g/m2, which prepared the surface to receive the second layer of gas barrier dispersion coating. After applying the first layer, it is dried by infrared heating and hot air convection. A second layer measuring approximately 2.5 g/m2 was applied over the first gas barrier coating, to form a total 2-layer gas barrier coating of approximately 5 g/m2. After applying the second layer, it is dried by infrared heating and hot air, and finally, the solidified resin is cooled to a temperature below 40 °C, to prevent bonding between sheets of paper with a barrier already applied on the surface (bonding the sheets with the resin still active, without cooling).

The applied quantity was limited to 2.5 g/m2 per partial layer to avoid excess water buildup on the cellulose-based substrate. The use of pre-coated paper as described in Figure 7 allows for greater control over dimensional stability, as the flexible pre-coating B acts as a surface primer and also impacts the roughness and porosity of the substrate surface.

The application technology used to form this gas barrier coating was a bar coating method. A bar diameter of 24 mm was used. The bar used to apply the barrier dispersion rotated in the same direction as the paper winding at a speed of 20 to 80 rpm, or in the opposite direction to the paper winding at a speed of 80 to 160 rpm.

Example 7

The paper substrate K from Table 1, as well as the substrate paper type best tested above for carrying oxygen barrier coatings, i.e. a greaseproof paper "Superperga WS 32 g/m2 Parchment FL109" from Nordic Paper, were for comparison (Comparative Example 1), were laminated in the same way with LDPE on their respective top sides at 20 g/m2.

The comparative paper was measured to have a surface roughness on the top side, i.e., the side to be coated with the barrier, of approximately 36 ml/min Bendtsen. It comprised higher-grade refined cellulose, i.e., cellulose with smaller fibrous/fibrillar molecules, to provide its dense surface area and an average paper density of just 865 kg/m3. The comparative paper is not 100% recyclable, but it does leave a reject of water-swollen, low-molecular-weight cellulose.

The paper substrate K used in the invention had a Bendtsen roughness on the upper side of approximately 20 ml/min.

The oxygen transmission rates through the flat laminated papers of Example 1 and Comparative Example 1 were measured using a coulometric detector and the evaluation was performed in accordance with ASTM F1927-14 using the unit cm3/m2/24 h at an oxygen pressure of 20.26 kPa (0.2 atm) and a humidity level of 50% relative humidity. The measurement results are presented in Table 6.

Table 6. TTO for PE laminated flat papers, cm3/m2/24 h at 20.26 kPa (0.2 atm), 50% RH

From the results in Table 6, it is observed that the best paper substrate studied above, as a laminated sample, provides better initial inherent TTO performance than the paper substrate pre-coated with the base layer of the invention.

The precoated paper substrates of Example 7 but without the LDPE laminate layers on both sides were therefore coated with a first gas barrier layer of polyvinyl alcohol, PVOH or NCC, respectively, over the ductile base layer precoat (top side of the paper substrate). The PVOH used was obtained from Kuraray and had a degree of hydrolysis of at least 98%, i.e., Poval® 6-98. The PVOH dispersion was applied by means of a soft roller coating method on pilot-scale equipment and the applied wet amount of the aqueous PVOH dispersion was approximately 15% by weight. For antifoaming purposes, 0.05% by volume of 1-octanol was added to the PVOH. The Brookfield viscosity at 23 °C of the PVOH dispersion barrier composition was 500-800 mPas.

The coating roller rotation speed was 160 rpm, rotating in the opposite direction to the web travel direction. The coating was applied in two stages, with dry weights of the first and second coats of 1.6 g/m2 and 1.6 g/m2, respectively.

A combination of IR irradiation and hot air was used to dry the coated layers and the surface temperature was kept below 100 degrees Celsius while the web speed was approximately 300 m/min during coating.

In a separate coating operation on the same pilot-scale equipment, an NCC dispersion was applied instead, using a smooth roll coating method. The applied amount of the aqueous NCC dispersion was approximately 19-20% by weight. The Brookfield viscosity at 23 °C of the aqueous NCC dispersion barrier composition was <2000 mPas, and the viscosity at 50 °C was 1000-1200 mPas. Both IR and hot air were used to dry the coated layers, and the web speed was approximately 300 m/min during coating. The coating roll rotation speed was 80 rpm, rotating in the opposite direction to the web running direction. The coating was applied in two stages, with dry basis weights of the first and second coats being 1.9 g/m2 and 2.7 g/m2, respectively.

The pre-coated and gas barrier coated papers were then laminated with 20 g/m2 LDPE on their top sides, and the oxygen transmission rates were evaluated as in Example 7 and Comparative Example 1, but also including a humidity level of 80%. The oxygen transmission rates are shown in Table 7.

Table 7. TTO for pre-coated and barrier coated papers laminated with PE.

From the results in Table 7, it is observed that the TTO performance of the precoated and barrier-coated paper is significantly improved compared to the precoated paper without a gas barrier coating in Table 6. Both the PVOH coating and the NCC coating improve TTO performance. However, both coating types are sensitive to humidity, with higher TTO at 80% RH compared to TTO at 50%.

Example 8

The precoated and dispersion-coated gas barrier papers of Example 7 were metallized to an optical density of approximately 1.8. The metallized barrier papers were then extrusion-coated with paperboard and polymers to provide a packaging material with the following structure:

//Outer LDPE 12 g/m2/ Duplex CLC 80 mN, 200 g/m2, cardboard main layer/LDPE bond layer 20 g/m2/paper substrate with barrier coating

(with 2x barrier coating ~4 g/m2/ Al metal DO ~1.8/ Adhesive layer EAA copolymer 6 g/m2/ LDPE+m-LLDPE combination 29 g/m2//

The liquid board was creased before lamination to facilitate subsequent folding of the packaging. The packaging material was laminated on a flexible pilot laminator with three extrusion coating stations. The lamination speed was approximately 400 m/min.

The CLC Duplex board was a conventional clay-coated board, and the m-LLDPE is a metallocene-catalyzed linear low-density polyethylene. The barrier-coated side of the paper substrate was directed inward in the laminate structure (corresponding to the interior of a packaging container made from the laminate). The EAA adhesive polymer and the innermost heat-sealable layer were coextruded together onto the barrier-coated paper, and the outermost LDPE layer was extrusion-coated onto the outside of the board.

Oxygen transmission rates through the flat laminated packaging materials of Example 8 were measured using a coulometric detector and testing was performed in accordance with ASTM F1927-14 using the unit cm3/m2/24 h at 20.26 kPa (0.2 atm) oxygen pressure and humidity levels of 50% and 80% relative humidity.

Comparative Example 2

The paper substrate tested above was also used in Comparative Example 1, coated with a gas barrier and laminated to a packaging material structure in a substantially corresponding manner, except that the ductile base layer precoat is not included.

The paper was first coated in two consecutive dispersion coating operations with 1.5 g/m2 of PVOH (Poval® 15-99, fully saponified PVOH) each, with drying after each step. It was then metallized to an optical density of approximately 2.3.

The comparative paper substrate with barrier coating was further laminated to a packaging material structure as follows:

//Outer LDPE 12 g/m2/ Duplex CLC 80 mN, 200 g/m2, cardboard main layer/LDPE bond layer 20 g/m2/paper substrate with barrier coating

(with 2x barrier coating ~1.5 g/m2/ Al metal DO ~2.3/ Adhesive layer EAA copolymer 6 g/m2/ LDPE+m-LLDPE combination 19 g/m2//

The results of TTO measurements on the laminated packaging materials of Example 8 and Comparative Example 2 are presented in Table 8.

Table 8. TTO for flat laminated packaging materials

* Measured at oxygen pressure 101.32 kPa (1 atm)/20.26 kPa (0.2 atm)

** Converted to oxygen pressure of 20.26 kPa (0.2 atm)

It can be seen in Table 8 that the TTO values for the packaging material using a pre-coated and barrier-coated paper are higher than for the packaging material using a highly refined greaseproof paper, although the grammages of the barrier coating were higher for the pre-coated paper of the invention. This may be attributed to the fact that the TTO contribution of the paper itself is lower for the pre-coated paper compared to the highly refined greaseproof paper, see Table 7.

It is also observed that packaging material using pre-coated and barrier-coated paper is not sensitive to higher humidity levels.

Example 9

Cartons were produced on a Tetra Pak® E3/CompactFlex filling machine. This type of filling machine can fill portioned cartons at a speed of 9,000 cartons/hour and is flexible enough to quickly changeover between different carton formats. The cartons were Tetra Brik® format with a volume of 200 ml.

The oxygen transmission rate of the containers (full, empty, and dry) was measured with containers mounted on a special stand; nitrogen is purged inside the container; the exterior of the container is exposed to the environment surrounding the instrument. When oxygen penetrates through the container into the nitrogen carrier gas, it is transported to the coulometric sensor. The sensor reads the amount of oxygen leaking into the nitrogen gas inside the container. The TTO is then evaluated according to ASTM F1307-14, at 20.26 kPa (0.2 atm) (surrounding air containing 21% oxygen). The unit of measurement is cm3/container/24 h.

Table 9. TTO for packaging, including loss factors.

*Using the laminated area of the packaging and the corresponding TTO value for flat packaging material in Table 2.

It is interesting and surprising to see from Table 9 that although the TTO values of flat laminated packaging materials using pre-coated and barrier coated paper are higher than those of flat laminated packaging materials using a highly refined greaseproof paper, as seen from Table 7, the TTO values of the package are improved by the use of pre-coated and barrier coated paper. The measured TTO of the package is 0.013-0.016 cm3/package/24 h/20.26 kPa (0.2 atm) instead of 0.075. Dividing the measured TTO values with the corresponding theoretically calculated ones also shows that the loss factors are close to 1 when using pre-coated and barrier coated paper, compared to a loss factor of 9.6 when using a highly refined greaseproof paper. It is evident that the gas barrier performance of flat-laminated packaging material is maintained even after folding, when using pre-coated and barrier-coated paper. This is attributed to the ductile base layer precoat, which is able to reduce the effect of stress concentrations in the paper. Stress concentrations can also be the source of cracks and their propagation through the paper. If the paper cracks, a very thin barrier layer is unable to withstand the high stress and, consequently, will also crack, thereby losing the gas barrier. Ductile materials, in particular, are able to withstand high elongations and are able to redistribute stress concentrations in the paper during folding.

Additionally, in relation to the attached figures:

An embodiment of a barrier-coated cellulose-based substrate 10a of the invention is shown in cross-section in Figure 1a. The substrate 11a is a paper made from a majority proportion of sulfate softwood pulp cellulose fibers, with a basis weight of 35 g/m2, first provided with a ductile base layer precoat 12a on its upper side, by applying a latex or biopolymer binder composition, such as, specifically in this example, a latex binder composition SB further comprising an inorganic sheet filler, by means of aqueous dispersion coating and subsequent drying to evaporate the water. The dry weight of the applied ductile base layer precoat is approximately 12 g/m2. Optionally, a further second ductile coating 15a, of the same composition as the ductile base layer precoat 12a, may be applied in the same manner to the opposite uncoated side of the paper substrate 11a. The dry weight of the second ductile coating is approximately 5 g/m2. The thus precoated paper substrate is subsequently supercalendered by passing through several high pressure roll nips and at least one heat roll applying a surface temperature of 100 to 240°C.

Additionally, the paper substrate has a gas barrier coating 13a made of a barrier dispersion or solution coating of PVOH, Poval® 6-98 from Kuraray, applied onto the surface of the ductile base coat precoat 12a. Therefore, the gas barrier coating 13a is applied by means of aqueous dispersion coating and subsequently dried to evaporate the water, preferably as two consecutive partial coating steps with drying in between and afterwards. The total dry weight of the PVOH barrier dispersion coating is approximately 3.5 g/m2. Additionally and optionally, the barrier dispersion coated paper substrate may have an aluminum barrier deposition coating 14a, i.e., a metallized layer of aluminum, applied over the dry surface of the barrier dispersion coating 13a, and by physical vapor deposition at an OD of approximately 1.8.

In Fig. 2a, a laminated packaging material 20a for liquid carton packaging is shown, wherein the laminated material comprises a main layer 21a of paperboard, having a flexural strength of 80 mN and a basis weight of approximately 200 g/m2 and further comprising an outer heat-sealable, liquid-impermeable layer 22a of low-density polyethylene applied to the outside of the main layer 21a, which side is to be directed toward the outside of a packaging container made from the packaging laminate. The layer 22a is transparent to show the printed decoration pattern 27a, applied onto the main paper or paperboard layer, to the outside, thereby informing consumers in retail establishments and grocery stores about the package contents, the package brand, and other information. The polyethylene of the outer layer 22a is a conventional heat-sealable grade low-density polyethylene (LDPE), but may also include additional similar polymers, including LLDPE. It is applied in an amount of approximately 12 g/m2. An innermost heat-sealable, liquid-impermeable layer 23a is disposed on the opposite side of the main layer 21a, which is to be directed towards the interior of a packaging container produced from the packaging laminate, i.e., the layer 23a will be in direct contact with the packaged product. The innermost heat-sealable layer 23a, which is to form strong transverse heat seals of a liquid packaging container made from the laminated packaging material, comprises one or more polyethylenes in combination selected from the groups consisting of LDPE, linear low-density polyethylene (LLDPE), and LLDPE produced by polymerizing an ethylene monomer with a C4-C8, more preferably C6-C8, alkylene alpha-olefin monomer, in the presence of a metallocene catalyst, i.e., called metallocene-LLDPE (m-LLDPE). This innermost layer of polyethylenes is applied in an amount of approximately 29 g/m2.

The main layer 21a is laminated to the uncoated side (i.e., not having any gas barrier coating applied) of the barrier coated paper substrate 10a of Fig. 1a, i.e., 25a, also having an aluminum barrier deposition coating 14a, i.e., a metallized layer of aluminum, applied over the dry surface of the barrier dispersion coating 13a, by physical vapor deposition at an OD of about 1.8, by means of an intermediate tie layer 26a of a low density polyethylene (LDPE). The intermediate tie layer 26a is formed by melt extruding it in the form of a thin polymer melt curtain between the two paper webs and thus laminating the main layer and the barrier coated paper substrate together, while the three layers pass through a cooled nip. The applied amount of the intermediate bonding layer 26a is approximately 20 g/m2.

The innermost heat sealable layer 23a may consist of one layer or alternatively two or more partial layers of the same or different types of LDPE or LLDPE or blends thereof, and is well adhered to the metallized barrier deposition coating surface 14a of the barrier coated paper substrate 10a by means of an intermediate coextruded tie layer 24a in an amount of about 6 g/m2 of, for example, ethylene-acrylic acid (EAA) copolymer, which thereby bonds the innermost heat sealable layer(s) to the barrier coated paper substrate 10a, the layers being applied together in a single melt coextrusion coating step of the layers 24a and 23a.

In order to reduce the amount of the thermoplastic polymer fraction in recycling processes, such as extrusion-laminated polyethylene polymers, and to improve the repulpability of the packaging material in recycling processes, the laminating layer 26a, which bonds the barrier-coated cellulose-based substrate 25a to the main layer 21a, may instead be a thin layer of a wet-laminated polymer binder obtained from the drying of a dispersion-coated aqueous adhesive composition. Such a laminating step is carried out in an efficient cold or room temperature lamination step at industrial speed without the need for any energy-consuming drying operations to accelerate water evaporation. The dry weight of such a bonding layer in such an embodiment would only need to be about 6 g/m2, or preferably less, and be made of a polymer that is readily redispersible in water so as to be repulpable in the cellulose fiber fraction in a paperboard fiber recycling process.

In a further embodiment, the back side of the paper substrate 11a may be first coated with a second ductile coating 15a, of the same or similar composition as the ductile base layer precoat 12a, having a dry weight of about 5 g/m2, as described in connection with Fig. 1a, and then the tie layer 26a may comprise an aqueous adhesive composition similar to the ductile base layer precoat 15a composition. In a separate embodiment, the paper substrate 11a may remain uncoated on the back side, although the amount of tie layer 26a may be higher, such as from 10 to about 12 g/m2, to simultaneously produce a single layer 26a, which behaves as both a ductile base layer 15a and a lamination tie layer 26a.

Alternatively, a primary layer 21a may be laminated to the uncoated side (i.e., not having any gas barrier coating applied) of the barrier coated paper substrate 10a of Fig. 1a, however, without having the optional aluminum barrier deposition coating 14a, by the same methods described above. Laminated to the interior of the barrier coated barrier substrate is a prefabricated polymer film substrate having a barrier deposition coating applied by a vapor deposition method, such as a metallization coating laminated to the barrier coated cellulose-based substrate. The polymer film substrate may be laminated to the barrier coated cellulose-based substrate by an interjacent tie layer of a polymer, either by extrusion lamination of a thermoplastic tie layer between the two barrier coated webs, or by wet lamination of an aqueous adhesive. The metallized polymer film substrate may comprise a layer of heat-sealable material on the side of the polymer film substrate facing away from the metallization coating, to form the second innermost heat-sealable, liquid-impermeable layer of material. Alternatively, the metallized polymer film substrate may be further extrusion-coated with the second innermost heat-sealable, liquid-impermeable layer 23a. Otherwise, the layers, materials, and polymers are the same as in the laminated packaging material of Fig. 2a and described above.

In still further embodiments of the laminated structure of Figure 2a (not shown), the innermost liquid impermeable layer 23a' may consist of a pre-made blown film, comprising LDPE or LLDPE polymers in any combination thereof, and may be laminated to the barrier coated paper substrate, to the surface of its barrier deposition coating, i.e., aluminum metallization, by means of an intermediate, melt extrusion laminated tie layer 24a, comprising a thicker tie layer of EAA than that used in Figure 2a, or a simpler tie layer of LDPE, which is 12 to 20 g/m2, such as 12 to 18 g/m2, thick.

Alternatively, the pre-made blown film 23a may be laminated to the metallized coating by means of a further wet lamination bonding layer of an aqueous adhesive of an acrylic (co)polymer adhesive layer 24a' at room (cold) temperature in an amount of 3 to 5 g/m2. As indicated above, if the barrier deposition coating 14a is not applied to the barrier coated paper substrate, a barrier deposition coating may instead be applied to the pre-made film by vapor deposition coating.

In Fig. 3a , an embodiment of a main aqueous dispersion coating process 30a is shown, which may be used to apply a gas barrier coating 12 from an aqueous gas barrier composition onto a substrate, or to apply a ductile base coat precoat from an aqueous latex composition. Alternatively, it may be used to apply an aqueous adhesive composition to wet-laminate two webs together, at least one of which has a fibrous cellulose surface. The cellulose-based substrate web 31a (e.g., the paper 11a of Fig. 1 a) is sent to a dispersion coating station 32a, where the aqueous dispersion composition is applied by means of rollers onto the upper surface of the substrate. The aqueous dispersion composition may have a water content of 80 to 99% by weight, % in the case of barrier compositions, therefore, there may be substantial water in the wet-coated substrate that needs to be dried by heat and removed by evaporation, to form a continuous coating, which is homogeneous and has uniform quality with respect to barrier properties and surface properties, i.e., uniformity and wettability. Drying is accomplished by a hot air dryer 33a, which also allows moisture to evaporate and be removed from the substrate surface. The temperature of the substrate as it travels through the dryer may be maintained constant at a temperature below 100°C, such as below 90°C, such as 70 to 90°C, in order to avoid defects in the coating. Drying may be partially assisted by heat radiated by infrared lamps, in combination with hot air convection drying. For ductile base coat precoat coating, however, the water content is much lower and therefore less drying will also be required.

A web resulting from a paper substrate 34a precoated with a ductile base layer may optionally be calendered by passing it through at least one high pressure roll nip, and then sent for cooling and further winding onto a reel for intermediate storage and subsequently subjected to gas barrier coating operations. The additional coating operations may be vapor deposition coating of a barrier deposition coating 14, or an additional dispersion coating operation of a gas barrier composition, as described above, to provide a barrier coated cellulose-based substrate.

Fig. 3b shows a process 30b for the final lamination steps in the manufacture of the packaging laminate 20a, of Fig. 2a, respectively, after that, the main layer 21a has been first laminated to the barrier coated cellulose-based substrate 10a of Fig. 1a, (i.e., 25a of Fig. 2a).

As explained in connection with Fig. 2a, the main layer paperboard 21a may be laminated to the barrier-coated paper substrate 10a; 25a by means of wet cold dispersion adhesive lamination, or by means of melt extrusion lamination. The adhesive may be applied by a method the same as or similar to that described in connection with Fig. 3a, however, requiring no drying or very little heating.

The resulting paper prelaminate web 31b is sent from an intermediate storage reel or directly from the lamination station for laminating the paper prelaminate. The unlaminated side of the main layer 21a, i.e. its printed side, is joined in a cooled roll nip 33 to a curtain 32 of molten LDPE polymer, which is to form the outermost layer 22a of the laminate, the LDPE being extruded from an extruder feed block and a die 32b. Subsequently, the prelaminated paper web, now having the outermost layer 22 as a coating on its printed, outer side, passes through a second extruder feed block and die 34b and a lamination nip 35, where a curtain 34 of molten polymer is joined and coated onto the other side of the prelaminate, i.e. onto the barrier coated side of the paper substrate 10; 25a. The innermost heat-sealable layer(s) 23a are therefore co-extrusion coated onto the inner side of the pre-laminated paper web to form the finished laminated packaging material 36, which is ultimately wound onto a storage reel, not shown.

These two coextrusion stages in the nip lines 33 and 35 of the rolling rollers can alternatively be carried out as two consecutive stages in opposite order.

According to another embodiment, one or both of the outermost layers may be applied at a pre-lamination station, where the co-extrusion coated layer is first applied to the outside of the main (printed) board layer or onto the metallization coating of the barrier coated paper substrate, and subsequently the two pre-laminated paper webs may be bonded together, as described above.

According to a further embodiment, the innermost layers of the liquid-impermeable and heat-sealable thermoplastic layers are applied in the form of a prefabricated film, which is laminated to the coated side of the barrier-coated paper substrate 10.

As explained in connection with Fig. 2a, said innermost layer 23a' may be laminated to the barrier coated paper substrate 10 by a wet cold dispersion adhesive lamination process or by melt extrusion lamination.

Fig. 4a is a schematic view of an example of a plant 40a for physical vapor deposition, PVD, of a metallic aluminum coating, on a web substrate of the invention. The dispersion-coated paper substrate 41 is subjected, on its coated side, to continuous evaporative deposition 40 of evaporated aluminum to form a metallized layer of aluminum, or alternatively to a mixture of oxygen with aluminum vapor to form a deposited coating of aluminum oxide. The coating is provided at a thickness of 5 to 100 nm, preferably 10 to 50 nm, to form the barrier-coated paper 43 of the invention. The aluminum vapor is formed from ion bombardment from an evaporation source of a solid piece of aluminum 42. For the aluminum oxide coating, some gaseous oxygen may also be injected into the plasma chamber through inlet ports.

Fig. 4b is a schematic view of an example of a plant 40b for plasma enhanced chemical vapor deposition, PECVD, coating, for example, of diamond-like hydrogenated amorphous carbon coatings on a strip substrate of the invention. The strip substrate 44a is subjected, on one of its surfaces, to continuous PECVD, of a plasma, in a plasma reaction zone 45 created in the space between the magnetron electrodes 46 and a cooled strip transport drum 47, which also acts as an electrode, while the substrate is driven by the rotating drum, through the plasma reaction zone along the circumferential surface of the drum, and subsequently wound onto a roll as a barrier coated strip substrate 44b. The plasma for deposition coating an amorphous DLC coating layer can be created, for example, by injecting a precursor gas composition comprising an organic hydrocarbon gas, such as acetylene or methane, into the plasma reaction chamber. Other gas barrier coatings can be applied by the same principal PECVD method, such as silicon oxide, SiOx, coatings, then starting from an organosilicon compound precursor gas. The PECVD plasma chamber is maintained under vacuum by continuously evacuating the chamber at outlet ports 48a and 48b.

Fig. 5a shows an example of a packaging container 50a produced from a packaging laminate. The packaging container is particularly suitable for beverages, sauces, soups, or the like. Typically, such a package has a volume of approximately 100 to 1000 ml. It may be of any configuration, but is preferably brick-shaped, having longitudinal and transverse seals 51a and 52a, respectively, and optionally an opening device 53. In another embodiment, not shown, the packaging container may be wedge-shaped. In order to obtain such a "wedge shape," only the lower portion of the package is formed by folds such that the transverse heat seal of the lower portion is hidden beneath the triangular corner flaps, which are folded over and sealed against the bottom portion of the package. The transverse seal of the upper portion is left unfolded. This way, the partially folded package remains easy to handle and dimensionally stable enough to be placed on a grocery store shelf or any flat surface.

Fig. 5b shows an alternative example of a packaging container 50b produced from an alternative packaging laminate. The alternative packaging laminate is thinner, having a thinner main paper layer, and is therefore not dimensionally stable enough to form a parallelepiped or wedge-shaped package, and is not formed by folds after transverse sealing 52b. The packaging container will still be a pillow-shaped pouch-like container and will be distributed and marketed in this form.

Fig. 5c shows a pitched-top package 50c, which is formed by folding from a pre-cut sheet or blank of laminated packaging material comprising a main layer of paperboard and the barrier-coated paper substrate of the invention. Flat-top packages may also be formed from similar blanks of material.

Fig. 5d shows a bottle-type package 50d, which is a combination of a sleeve 54 formed from a pre-cut blank of laminated packaging material, and a top 55, which is formed by plastics injection molding in combination with an opening device such as a screw cap or the like. Such packages are marketed, for example, under the trade names Tetra Top® and Tetra Evero®. These particular packages are formed by joining the molded top 55 with an opening device attached in a closed position to a tubular sleeve 54 of laminated packaging material, sterilizing the bottle cap capsule thus formed, filling it with the food product, and finally folding down the bottom of the package and sealing it.

Fig. 6 shows the principle described in the introduction to the present application, i.e. a web of packaging material is formed into a tube 61 by overlapping the longitudinal edges 62, 62' of the web and heat sealing them together, thereby forming an overlapping seam 63. The tube 64 is continuously filled with the liquid food product to be packaged and divided into individual filled packages by repeated double transverse seals 65 of the tube at a predetermined distance from each other below the level of the contents filled in the tube. The packages 66 are separated by cutting between the double transverse seals (top seal and bottom seal) and finally formed into the desired geometric configuration by forming creases along fold lines prepared in the material.

Fig. 7 shows the effect of surface roughness on the oxygen transmission rate of the coated papers listed in Table 2, at 70% RH (ml/m2.day).

Fig. 8 shows the main structure of a ductile cellulose-based substrate A, as pre-coated with a ductile base layer pre-coating B on its upper side, and additionally optionally coated with a similar ductile coating C on its back side.

Claims (26)

1. Cellulose-based substrate (10a) with barrier coating, for use as a gas barrier sheet in a laminated packaging material for oxygen-sensitive products, comprising a cellulose-based substrate (11) having a density of at least 900 kg/m3 and a basis weight of 30 to 80 g/m2, and applied on a first side of the cellulose-based substrate, at least one gas barrier coating (13a, 14a) of at least one gas barrier material at a total thickness of 2 to 7000 nm, such as 2 to 5000 nm, such as 2 to 4000 nm, the gas barrier material excluding nanocrystalline cellulose, NCC, wherein the barrier-coated cellulose-based substrate (10) comprises a ductile base layer precoat (12a), which is applied by means of dispersion coating and subsequent drying, onto the surface of the first side of the cellulose-based substrate (11) and is positioned beneath the at least one gas barrier coating (13a, 14a), wherein the at least one gas barrier coating (13a, 14a) comprises a barrier dispersion coating (13a), first applied by means of dispersion or solution coating onto the ductile base layer precoat, and a barrier deposition coating (14a), subsequently applied by means of a vapor deposition method, onto the barrier dispersion coating, the barrier dispersion coating (13a) being applied in a total amount of 0.2 to 5 g/m2, by dry weight, the barrier deposition coating being a vapor deposition coating of a material selected from metals, metal oxides, inorganic oxides and carbon coatings, and being applied at a thickness of 5 to 200 nm, the ductile base coat precoat (12a) being obtained from an aqueous latex composition, such as a latex selected from the group comprising styrene-butadiene latex (SB latex), methylstyrenebutadiene latex, styrene acrylate latex (SA latex), acrylate latex, such as vinyl-acrylic copolymers and vinyl acetate acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadiene-acrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, mixtures thereof, or bio-derived latex made from polymeric materials of plant origin, the polymeric materials of plant origin being selected from the group comprising starch derivatives, including modified starches and starches crosslinked, polyisoprene, lignin-based polymers, alginates and gums such as guar gum and soy-based proteins, and is applied at a grammage of 2 to 15 g/m2, dry weight, the barrier-coated cellulose-based substrate being therefore suitable for providing gas barrier properties in a laminated packaging material and in packages made therefrom. 2. Cellulose-based substrate (10a) with barrier coating according to claim 1, wherein the barrier dispersion coating (13a) comprises a polymer selected from the group consisting of vinyl alcohol polymers and copolymers, such as from the group consisting of polyvinyl alcohol, PVOH and ethylene vinyl alcohol, EVOH, starch and starch derivatives, xylan, xylan derivative, nanofibrillar/microfibrillar cellulose, NFC/MFC, and combinations of two or more thereof. 3. Cellulose-based substrate with barrier coating according to any one of claims 1 or 2, wherein the barrier dispersion coating (13a) is applied in a total amount of 0.2 to 4 g/m2, more preferably 0.5 to 4 g/m2, such as 0.5 to 3.5 g/m2, such as 1 to 3 g/m2, by dry weight. 4. Cellulose-based substrate with barrier coating according to any one of claims 1-3, wherein the barrier dispersion coating (13a) is applied as two partial layers or "partial coatings", each layer being suitably applied in amounts of 0.2 to 2.5 g/m2, preferably 0.5 to 1.5 g/m2. 5. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the barrier deposition coating (14a) is applied by means of physical vapor deposition (PVD) or chemical vapor deposition (CVD). 6. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the barrier deposition coating (14a) is applied at a thickness of 5 to 100 nm. 7. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the barrier deposition coating (14a) is an aluminum metallization coating. 8. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the barrier deposition coating (14a) is an aluminium metallization coating which is applied at an optical density OD of 1.8 to 2.5. 9. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the ductile base layer precoat (12a) further comprises a filler material, such as an inorganic filler. 10. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the ductile base layer precoat (12a) comprises 4 to 45% by weight, such as 4 to 35% by weight, such as 4 to 25% by weight, such as 4 to 20% by weight, such as 4 to 16% by weight of the polymeric binder material having inherent ductility properties, and 55 to 96% by weight, such as 65 to 96% by weight, such as 75 to 96% by weight, such as 80 to 96% by weight of a filler material, on a dry weight basis and optionally additional compounds, such as thickening agents and crosslinking compounds, in additive amounts. 11. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the ductile base layer precoat (12a) comprises by dry weight 10 to 20% by weight of the polymeric binder material having inherent ductility properties, 75 to 85% by weight of an inorganic filler, 3 to 5% by weight of a crosslinking compound, such as starch, and 1 to 2% by weight of a thickening agent. 12. Cellulose-based substrate with barrier coating according to any one of claims 9-11, wherein the filler material is an inorganic layered compound, such as bentonite or kaolin. 13. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the ductile base layer precoat has a grammage of 5 to 15 g/m2, such as 8 to 15 g/m2, such as 10 to 15 g/m2. 14. Cellulose-based substrate (10a) with barrier coating according to any one of the preceding claims, wherein the cellulose-based substrate has a second ductile coating (15a) on its opposite side, such as of the same composition as the ductile base layer precoat (12a). 15. Cellulose-based substrate (10a) with barrier coating according to any one of the preceding claims, wherein the cellulose-based substrate with the ductile base layer precoat has an ash content of 15 to 25% by weight, such as 15 to 23% by weight, as determined by ISO1762:2019. 16. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the cellulose-based substrate including the ductile base layer precoat (12a) is calendered to an air permeability value of less than 100 nm/(Pa.s), which is the lower limit of applicability of the test method ISO 5636-5:2013, and further less than 1 nm, such as 40 to 900 pm/(Pa.s), such as 40 to 800 pm/(Pa.s), such as 100 to 700 pm/(Pa.s), such as 200 to 500 pm/(Pa.s), as determined by standard Sc An-P 26:78. 17. Cellulose-based substrate (10a) with barrier coating according to any one of the preceding claims, wherein the cellulose-based substrate including the ductile base layer precoat (12a) and the at least one gas barrier coating (13a, 14a) has a PPS surface roughness of less than 3.0 gm, such as less than 2.8 gm, such as less than 2.5 gm, such as less than 2.2 gm, such as less than 2.0 gm, such as 1.8 gm or less, as measured in accordance with TAPPI standard 555 om-15, which is the same as ISO standard 8791-4. 18. Cellulose-based substrate with barrier coating according to any one of the preceding claims, wherein the cellulose-based substrate comprises at least 50% by weight, such as 60 to 100% by weight, such as 70 to 100% by weight of softwood cellulose, such as Kraft softwood cellulose. 19. Method of manufacturing a cellulose-based substrate (10; 25a; 43; 44b) with a barrier coating according to any one of claims 1-18, comprising a) a first step of providing a cellulose-based substrate, having a first side and a second side, as a moving web (31a) in a roll-to-roll system, b) a second step of applying (32a) a first aqueous dispersion of a ductile base coat precoat composition, onto the first side of the movable cellulose-based substrate (31a), optionally applying a second aqueous dispersion of a ductile coating composition onto the other side of the movable substrate and drying (33a) the applied ductile base coat precoat, and the optional second ductile coating composition, by forced evaporation, c) a third step of calendering the pre-coated and drying cellulose-based substrate from step b) to obtain a density of at least 900 kg/m3, such as at least 1000 kg/m3, and d) a fourth step comprising a first step of applying a gas barrier coating by dispersion coating (32a') of a second dispersion or solution of a barrier composition, onto the first side of the movable cellulose-based substrate with the ductile base layer precoat (12a) and drying (33a') the applied gas barrier coating by forced evaporation and a second subsequent step of vapor deposition (40a; 40b) of a barrier deposition coating onto the first side of the movable cellulose-based substrate with the ductile base layer precoat (12a) and the gas barrier coating (13a) of the first step (13a), at a total gas barrier coating thickness of 2 to 7000 nm, such as 2 to 5000 nm. 20. Method according to claim 19, wherein the first aqueous dispersion of the ductile base coat precoat composition (12a) is applied in the form of an aqueous latex composition comprising a latex selected from the group comprising styrene-butadiene latex (SB latex), methylstyrenebutadiene latex, styrene acrylate latex (SA latex), acrylate latex, such as vinyl-acrylic copolymers and vinyl acetate acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadiene-acrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anhydride latex, mixtures thereof, or bio-derived latex made from polymeric materials of plant origin, the materials being selected polymers of plant origin from the group comprising starch derivatives, including modified starches and crosslinked starches, polyisoprene, lignin-based polymers, alginates and gums, such as guar gum and soy-based proteins. 21. Method according to any one of claims 19 and 20, wherein the first aqueous dispersion of the ductile base coat precoat composition (12a) further comprises a filler material. 22. Method according to any one of claims 19-21, wherein the pre-coated and dried cellulose-based substrate of step b) is calendered in the third step c) to obtain an air permeability value of less than 100 nm/(Pa.s), which is the lower limit of applicability of the ISO 5636-5:2013 test method, and furthermore less than 1 nm, such as from 40 to 900 pm/(Pa.s), such as from 40 to 800 pm/(Pa.s), such as from 100 to 700 pm/(Pa.s), such as from 200 to 500 pm/(Pa.s), as determined by SCAN-P 26:78 standard. 23. Method according to any one of claims 19-22, wherein in the third step c) the pre-coated and dried cellulose-based substrate of step b) is calendered to obtain a PPS surface roughness of less than 3.0 pm, such as less than 2.8 pm, such as less than 2.5 pm, such as less than 2.2 pm, such as less than 2.0 pm, such as 1.8 pm or less, as measured according to TAPPI standard 555 om-15, which is the same as ISO standard 8791-4. 24. Method according to any one of claims 19-23, wherein the ductile base coat precoat (12a) is applied as an aqueous latex composition having a solids content of 48 to 51% by weight and a Brookfield viscosity of 100 to 1000 mPa.s, a pH of 5.5 to 8. 25. Method according to any one of claims 19-24, wherein the pre-coated and dried cellulose-based substrate of step b) is supercalendered in step c). 26. Method according to claim 25, wherein the supercalendering is carried out by 3 to 8 roll nips, such as 4 to 8 roll nips, at a nominal nip pressure of at least 100 kN, such as at least 200 kN, such as 300 kN or higher and at a heat roll surface temperature of 100 to 300 °C, such as 100 to 240 °C.